It's no secret that games have become more and more online focus, games that can only be played online, games that require an online account, too much focus on multiplayer and leave single player behind, etc.
So with this in mind, in a few decades, can we still play these games? Unless a community survives for decades, at some point in time, the servers are going to be shut down. When that happens you won't be able to play those games, either in its entirety or the multiplayer part, but given the direction games are going, what's the point of playing Call of Duty for the single player for example.
This has nothing to do with DRM (even though that is part of the problem), but more the way developers are building their games and how many features will be lost in the future. In a few decades maybe no one will know what World of Warcraft is, won't be able to play a certain game because it requires an Origin or Uplay account, not being able to play multiplayer. You get the point.
The way technology is advancing will also be a problem, think of games like Grim Fandango which is a pain in the ass to play today, really amazing game that set boundaries at the time and A LOT of gamers don't know of its existence.
But previous gen games aren't that much of a problem because emulation and VC are somewhat solutions to this problems, the problem is in a few decades with current games. Emulation won't solve this problem easily, or if it fixes it, it won't be the same experience.
TL;DR: check this video, it explains the problem very well.
Nintendo and PC gamer
