So far none of the 44mm systems that are in a fixed body, x1d, gfx, Leica s, 645z, have been able to meet my needs for the photography in the areas that drew me medium format.
I would love to see a tiny body with evf work for me... but until then a tech cam, laptop, and modular setup with leaf shutters has the advantage.
I can see in the future 44mm potentially taking the place of the high end 36mm sector. This assumes 23mm and 17mm mirrorless cameras reach a focusing level that equals the sports cameras. My own personal work has been a mix of between m43 and mf...nothing in the middle has offered anything extra.
I am curious to see where mp counts level off as we reach higher up though. 16 - 24 is a sweet spot for a good majority of users. 100+ is really too much for general photography. I would never want to shoot a family birthday with a medium format camera at 50+ mp no matter how small and convenient the camera is.
I appreciate the answers about the factors in favor of "medium format" over smaller formats like 36x24mm, but most or all address the case a 54x40mm "full-sized digital medium format sensor" in a modular digital back, so that it is usable either with an OVF body or on a technical camera with shifts, tilts and such.
My follow-up question:
How does the reasoning change when it is a 44x33mm sensor in a body with an EVF instead of an OVF, as with the new offerings from Hasselblad and FujiFilm?
(BTW, one point I have not seen mentioned lately is flash sync at all speeds, offered by the leaf shutter lenses of some but not all MF systems.)