200mp doesn't seem like an insane amount of pixels to me; it's just more firmly in 8x10 film territory than 150mp has been, thus giving a respective photographer the benefits of such. From a practical standpoint, I think cropping latitude is a notable advantage, especially in conjunction with printing, say, 44inches and larger on the short side. Being able to have a bit of stand-off distance from the subject, yet still have the capability to print large solves a host of issues - several issues being depth-of-field issues (e.g. Being able to shoot f8-f11 and still having a decent amount of "depth" to work with), and more composition freedom... what one may think is an optimum composition, may not be what's optimum to another party or when using a photo for another application.
From a practical standpoint (price notwithstanding), having 200-400mp (equates to run-of-the-mill 8x10 film detail in my mind), coupled with a larger sensor size (i.e. 54x40'ish) yields a lot of utility... stand off / cropping capability + wider view (per each given lens) in close confines when compared to the same with a 44x33mm sensor equipped camera. It will be interesting to see what new MF model comes down the pipe.
Whatever new camera debuts, I hope it can compete with Phase's IQ4's useful features. I'd highly encourage folks to read the IQ4's manual from cover to cover to get an idea of just how feature rich Phase's IQ4 really is. I don't think anything else comes close, even today. The price however...