As you are probably aware, most video games are not sold forever. That is, they are sold for a limited time. This limited time can be months to years, but it is limited. Eventually, production of the game ceases and all stock is purchased.
For example, you'd be hard pressed to find a brand new copy of Pokémon: Gold Version being sold at a Wal-Mart or a Target in-store. If you wanted that game, you'd have to turn to the secondhand (used) market, such as eBay or Amazon, to buy a copy of the game. However, the fact that you can is sort of a marvel on its own, as some developers have compared buying used games to piracy, stating that buying a used game is no better or, heck, worse than piracy due to the fact that the developer does not receive a cut.
Video game streaming as DRM
A while back before the Xbox One launched, the Xbox One was announced to have a number of DRM restrictions in place, including having to pay a fee to play used games. Of course, that never happened because people complained, and they were heard.
But let me tell you something: that should've been taken as a warning. I assure you that this won't be the last time console makers try to impose insane anti-consumer practices on you like this. However, the next time this happens, you might not even notice.
So how does this tie into video game streaming? Video game streaming is a convenient way to play video games, especially on a device that cannot actually run the game. The device instead sends inputs to a server which responds with a video feed. There are a few caveats, with the main ones being input lag and video quality. If you have a very good connection, the input lag won't be quite as bad, and you can send a higher quality image.
However, it also kills not one, not two, but actually three birds with one stone: cheating, piracy, and used games.
Cheating: All you receive is a video feed, and you only have a limited number of inputs to the game. This means you can't do anything outside of the confines of the game, nor do you have any information that a regular player wouldn't have (besides screen peeking), thus you must play by the rules to win.
Piracy: Because all you receive is a video feed, you can't just take that video feed and turn it back into a video game. Sure, you can watch a recording you made, but you'd never be able to replay the game with just that.
Used games: And because you can't replay the game with a video feed, this means that the only way to play the game is to obtain access to it from the host's mainframe. Digital-only games mostly remove this, too, but streaming makes this completely impossible.
Here's the thing: As I pointed out, video games are not sold indefinitely. Often times, licenses expire, new systems come out, or Nintendo made it. Either way, a video game's life on store shelves is finite, and this is normal. If a game is popular, a remaster or re-release may even be made years later, but if not, then that release is the only way you can experience the game.
For physical releases, you can still buy the game secondhand or get it from someone as a gift, provided you have a compatible system for it. In most cases these games will be sold at a significant discount, but there are some games that end up being sold for well over their original price. Some games, like Paper Mario: The Thousand-Year Door or Pokémon: Emerald Version, get sold used for a 50% to even a 150% markup from the original MSRP.
Either way, the original publishers or developers will see none of the profits from that since the game was already sold for the original $40-$60. As mentioned previously with the original Xbox One's completely insane DRM plans, some developers do not like that physical media has that side effect of being able to be resold without the original developers making a cut.
Games only obtainable as digital only, of course, are a lot harder to obtain once they're no longer sold, but for many games, such as with Flappy Bird, people will find a way. But in most cases, that's it. The game more-or-less dies with the hardware it's on unless you find a way to extract it and play it on other hardware.
Digital vs. Streaming
It's no secret that publishers have been pushing for digital releases a lot more. Nintendo, for example, gives you 5% of the game's cost towards your next purchase every time you buy a game on the eShop, but they only give you 1% if you buy it physical, and said physical copy has to be purchased within a year of the game's release. After all, they receive a greater cut of the profits without retailers being a middle man, and they don't have to pay extra for physical media. And, of course, if you buy a game digitally, it's difficult to resell it. When said game is no longer sold, then unless you find someone with a console that has the game on it, it's going to be pretty hard to play the game (legally).
Video game streaming is this but worse. Now when a game is no longer being produced, that's it. No more game. For anyone. That version of the game is basically permanently obliterated from history, and yes, even if you paid for the game, you don't have access to it anymore, and unless there was a release that wasn't stream-only, you're never playing it again. And, of course, unlike digital only games, this also fixes the aforementioned "piracy" and "cheating" points.
Digital only games
It used to be with PC games, you had to buy an installation disc for the game. I still have my jewel case for the Warcraft III Battle Chest among other CD-based games like Halo: Combat Evolved or Call of Duty Modern Warfare. All of these are fairly old games.
Today, most sales are digital sales and most publishers do not even bother making a physical copy. I imagine this is because most PC gamers are content with being completely digital-only. After all, a lot of PCs don't even have optical discs! My PC sure doesn't.
I do see a few PC games at the store here and there, like Wolfenstein II: The New Colossus which I saw for $40 at Wal-Mart the last time I was there. However, there's hardly any section for PC games, where there used to be one. I imagine this will one day be the case with consoles, too, but not any time soon since physical media still sells really well.
Streaming only games
Logically, the next step for digital only games is streaming only games, as it's even more convenient than digital only games (that you don't stream). After all, anything can be a streaming client, and with phones having better wireless Internet connectivity, you can theoretically play a full AAA game anywhere via streaming.
Right now, there aren't any major games that are streaming exclusive. I think the main reason this hasn't taken off is because most people do not have good Internet service providers, so the experience of playing a game streamed is still pretty inferior to the experience of playing the game normally, especially if you live an area with a slow Internet connection. So, um... thank you, low quality ISPs, for being hot garbage. You are actually doing us all a service by being terrible, low quality, overpriced trash heaps. Keep up the good work!
However, I predict that, one day, even the "cheap" Internet connections will be enough to stream games without any noticeable hitches. As a result, I believe that more games will become exclusive to streaming, just like how most PC games are exclusive to digital only right now. Maybe not all games will be stream-only, but I do think some will, and when those games are no longer streamed, they will be deleted from history. So, no nostalgia fix for you with that game, where I can play Pokémon: Gold Version decades after it came out (after replacing the battery), because your favorite game actually no longer exists (unless they Disney Vault it and try to sell it to you again for another limited time).
And unlike what happened with the Xbox One, many people probably won't be complaining about games becoming streaming only. After all, most people seem to have embraced digital games pretty quickly, and streaming is the logical next step for it. And hey, I'm sure people will love that they now have the convenience of playing AAA games from a phone.
But make no mistake: we'll be going full circle to the mainframe model, giving up basic freedom like being able to resell our games (or even merely replay them) in the name of convenience. Ownership won't exist, though I suppose one will argue you never owned the game but the right to play said game, instead. Which I say that, with video game streaming, it seems they can revoke the right at any time for any reason or even no reason.
This could be soon. This could be later. I don't know, but I'm certain it will happen. And if it never happens, please let me know as I will gladly eat my words with the loudest of chewing sounds. OM NOM NOM.
Maybe streaming only games are not worth worrying about it, since if it's going to happen, it'll happen, but I urge you to consider not supporting video game streaming if you can. There may come a time where your favorite game will only be accessible from streaming, and honestly, I wouldn't blame you for wanting to play it, but if you can, don't stream it. Play games on a system that is actually running the game whenever possible and not a dumb terminal.