IMAX is DOOM.

[SvennoJ]

Waiting for 8K content will take a while. Japan has plans to implement 8K broadcasting from 2016 to 2020.
http://sploid.gizmodo.com/8k-tv-films-arrive-to-japan-and-they-feel-like-looking-1464050347
But considering how our infrastructure can't even handle good quality 1080p it might be a long wait.

There is plenty of 4K content already, as you said movies from 2010 and onwards are 4K digital, anything before 2000 is 4K 35mm.

IMAX only has documentaries on 70mm plus these are all the 70mm movies ever made:
http://en.wikipedia.org/wiki/List_of_70_mm_films
I guess if you like soviet movies, you'll have a great selection of 8K content.

On the other hand, 8K prototypes have already been shown at CES. It might not be that long until they appear next to 4K tvs. 4K might be the new Ultra HD ready standard. I just wonder how you're going to get native content on an 8K tv.

Anyway for IMAX, invest in NHK's 8K 120fps cameras, and set up dual 8K projectors on huge screens with 22.2 surround sound, that will justify the higher ticket price again.