Getting better sensor uniformity would be one important thing to me, reducing colour aberrations.
For the work I do, medium format really needs to write some presets or change their color response.
All of digital is somewhat flaky compared to film in the way it picks up ambient color and all of digital is so tilted towards holding the highlights and shadows even the dslrs look somewhat flat, but this (and I'm not a color scientist) makes for a lot of color contamination (or better put it digital sees everything and the medium format backs see too much for what I do).
Film was different in the fact it was kind of dumb, it didn't seem to see everything. With film I was always adding fill and with digital I would rather start in black and work my way to white.
The medium format files are the most problematic. When they are on they are completely amazing and if your working with controlled lighting under the conditions they seem to be designed for they hold detail, highlights, shadows like no dslr can, but when you are working with mixed lighting, like sunlight and hmi fill, or your working with very hard direct light in studio, they cast and require a lot of post work to get skin colors to the look you remembered in film.
Little things like high key, extreme low key and back light going to flare seem to make digital go crazy.
I assume that whoever writes the software/firmware/grey balances . . . whatever, is shooting color charts and vegtables but they really need to shoot under a lot of conditions and skin tones in almost every kind of light.
Last night I was putting together some pre production materials for a project and went onto the servers and pulled down images from the 1ds1, 1ds2, A-22, p30 and p30+.
Some were amazingly on, others were almost impossible to get that great skin color without working in photoshop. Once again when the medium format was ON it was amazing, but when off it requires selecting and almost painting the skin.
The most uniform of all the cameras was the original 1ds1. It had it's issues, but is was the most consistent.
As far as 60mpx, well that's up to whoever buys it. Personally I think it's just easier and sound bites better to claim more megapixels than it does to mention stable software, or show beautiful skin tone color, but these companies will do what they want and I guess there is value in bigger is better.
Regardless, why none of these companies have not hired some kid out of Art Center, send him on a week long shoot of 5 skin tones, all types of lighting, clothes and locations and had him shoot their digital backs, next to film and compared the results is beyond me.