The problem is at you going to get a fake-max screen size and price of EACH of these 4k projectors are comparable to new house.
I would get approx 15 k dedicated theater room could get you 99.9% of that experience with "humble" 1080p projector
I'd budget more like $15-20K, or a bit more depending on speaker choices and channel count for sound alone, 8-15K for picture, and bring the room itself in at 40K not counting special acoustic isolation, assuming you hired contractors and didn't just grab your own hammer and go nuts. For 99.9% of the home-IMAX experience you'd probably want to hit just over 100K including modest decor and acoustic treatment.
But I totally agree with your point. Ditch the projectors, and reallocate the bucks and get nearly the same thing for a fraction of the cost.
The puzzling part of this is, dedicated HT rooms of any kind make up a fraction of a percent of the total HT market right now, and the extreme high end is a fraction of that, so where's the market for this?