Well, that’s what Moore’s Law was for. The processing power does increase massively over each generation. It’s just that at this point better graphics are less noticeable. There is not much difference to the eye between 100.000 and a million or more polygons.
We’ve basically reached the top. Graphics fidelity is just down to what the artists do with it.
Damn, Valve going against fan projects is really weird. Especially considering that most of their biggest games are former mods. And they let just about anyone do something in the Half Life universe.
Depends on the game. When the game was made in a way that is easily moddable then installing mods usually just means putting the mod files into some directory. But when a mod is supposed to do something that is not really supported then it has to do even more crazy stuff. And when several mods want to do similar crazy stuff it gets even more complicated.
So it really depends. Though BG3 has mod support built in by now. So everything in there should be easy.