If/when Wayland works great, I'm sure more people will start using it. In the meantime, it still breaks stuff that people use.

X via ssh is still useful, and I will be unhappy with wayland implementations until desktop shells get usefully separated from compositors. They need to be able to die/crash/be restarted separately.

What are the upsides?

the vast majority of people with a nvidia gpu

I use X via ssh at least once a week