[Tracker]

You could technically setup a virtual desktop environment installing Windows XP or Win98 and its games and use some sort of remote desktop access to play games. I think this is the closest we can get to "old games playable in a browser". And probably this is the best way to do it moving forward.

Google Stadia already uses streaming technology, and I remember Gaikai used to be a very strong precursor (until Sony killed it off, it turns out).

Also Microsoft is toying with the idea of virtual PCs and Xbox Game Pass now allows you to stream games too. I can easily see GOG.com doing the same, especially since most old games don't need any reasonable hardware to run, the only bottleneck being bandwidth.