I would agree performance and application availability is the difference and as much as we would like to say nvidia is going to come out with some x86 killer its not going to happen that easily. Looking at apple will give you a good mark of what can be done with a bunch of reasourses and forced software adaptation.Games I'll give you. That's a really big hurdle to clear. But it's also not a market that can't be cleared: the biggest games are not the most graphically intensive games, even on the desktop, and with Nvidia graphics, I don't see it as impossible. Just not... soon.
What's the practical difference between an ARM Chromebook and a Windows x86 laptop?
To me, it's performance and application availability. The performance is what Nvidia is now in a position to address, and application availability from a strictly consumer perspective is a non-issue. Porting to ARM isn't going to be fast, but it's not going to be that difficult either.
I run x86 because it is massively vast that vastness does not come overnight and it does not come overtime if software is not forced to. It can for x86 as it was the sole practical arch for a very large period of time. It's simply not worth the investment for nvidia when they can throw that money at a server chip and not have to deal with any of that.
And to state my position on personally using a differnt arch I would happily fire up a power 9 rig if I had one and there would be very real things do do with it (including virtulizing x86 if you really want). This is because its a decently powerful chip. If such a arm chip like that existed it could fill a similar enthusiast/enterprise role but that is very far off from a mainstream desktop cpu