I realise this has been going a few days but just to throw a couple of my experiences into the ring-
The iPad mixing is good enough I think to make the X32 rack almost usable alone for a live situation. We have an X32 rack and a full sized X32 console, and even with the full console I still run an iPad by my side as I use the full console - as mentioned some of the features (EQs, some mon sends, etc) and just faster on the iPad than even on the full console.
The X32 rack does have front controls which in theory do give you adjustment of all the parameters, so you aren't in the dark, but you wouldn't want to operate by it. You might be able to do some clever things with little units like the BCF2000 to give control of 8 channels but I haven't tried that in the flesh yet.
The X32 and X32-Rack together do make a good pair, as the X32-Rack can be used as a stage box (in place of an S16), but unlike the S16 can also perform the proper processing duties for the gigs that are smaller than need the full X32 console, and can be run from an iPad.
The SM Pro Audio UMix series do look great, but we pre-ordered one, being assured a delivery date "within one or two weeks" - this was in August 2014 - they have been perpetually "one or two weeks from shipping!" for months now. The price point does look great though and the iPad interface is excellent, being designed for touchscreen from the outset rather than being a digital copy of an analogue layout (things like gain on sliders rather than onscreen rotary pots) - however since we found the iPad app of the Behringer so usable we cancelled the UMix pre-orders as we didn't want to have to get familiar with two apps if using the other manufacturer for the smaller gigs.
Man, sounds you got a really good thing going on there. I've heard about the delays with the UMix. I hope they get it off the ground.