To me, 33x44mm format is too small to "step up" from the 24x36 format, simply because the difference between 33x44 and 24x36 is much smaller than that between FX and DX. When the 4:3 format is trimmed to 3:2, the difference is even smaller.
I also consider Sony BSI 42MP sensor as game changer.
I remember Bjørn's review of D1. Its "lowly" 2.7MP sensor (see the decimal point?) already surpassed the resolution of Fuji Velvia 50.
We can look at it another way: If 24x36 is trimmed to 24x32 yielding a 4:3 aspect ratio, the difference between the two formats become 1.89. I think that the ultimate choice here will be a personal one based on taste. The 4:3 aspect ratio is closer to many classical MF and LF formats than the 3:2 of 35mm format and APS-C/DX sensors.
I agree also that the Sony 42mp BSI sensor is a game changer, but for many more reasons than just competing favourably with the 50mp sensor in the Fujifilm GF50s camera on image quality. It helps provide speed and versatility to the Sony A7RII and the Sony A99II, that you won't associate with a slower paced MF camera.
I think both 35mm and mini MF 33x44 will find their friends.