Yeah, that would be possible and then 35mm and IMAX 70mm would cut together at the same ratio, but it wouldn’t be utilising all of the 15/70 frame, so you might as well downgrade very slightly to 65mm cameras. IMAX is a square format, so if you matte it, you’re wasting a lot of dough on the square screen, the incredibly powerful bulb and the film stock itself.
Home video has gone the way of widescreen, so cinemascope looks better than 4:3 on all our screens, but if we had HD (or equivalent) square telly’s - IMAX would work great, and you’d shoot academy 35mm to go with it.

Now basically everything has to be 16:9 or wider, IMAX is kinda an aberrant format - but because it fills up most of your visual field (unlike cinemascope) it’s a genuinely unique experience, and can’t really be translated to home video.
Sorry to waffle on 😛