If Sony would make a MF body, I’d be all in.
As far as I'm concerned, the primes aren't particularly larger or heavier for MF than they are for FF, it's more that the higher resolution and larger sensor size creates physical limits that makes everything slower on MF. No 20fps burst shots in RAW at full resolution with a Fuji GFX100 II, it's only 5fps. That lack of speed is reflected everywhere, because it's doing it on a sensor that's twice the size and twice the resolution, but otherwise it seemed like a pretty amazing camera to me. Speed for me is important though, so I stuck with a Nikon Z8.
It sounds like an MF setup with say a 28mm and a 100mm equivalent lens would require more work but possible (though maybe not enjoyable) to casually carry around.
When shooting raw stills I don’t particularly care about speed. I do enjoy shooting raw CinemaDNG video, there are reasonably priced FF bodies that support it, but if I get a camera for high-quality stills FPS wouldn’t really be a deal-breaker for my uses (I guess it might for bird watching or for sports).
Not with true large format, but with the new Fuji medium format cameras it's starting to become reasonably possible to do faster work like wildlife at larger format sizes. The main issue remains, which is sensor readout speed, but the technology has gotten so much better that you can get results with things like birds-in-flight that are comparable to a FF DSLR camera from 10 years ago, with MF now, as far as speed, but at 3x-5x the effective resolution.
Cost is still prohibitive though, I recently upgraded and really considered the new Fuji 100MP MF line, but ended up with a Nikon Z8 in the end for wildlife. On my next iteration, I'll probably bite the bullet and go MF. If I could double the resolution and get similar speed, it'd be worth it, IMO. Especially at the sizes I typically print