I think from a manufacturer's standpoint there is too much redundancy to support a different flavor of device (there is going to be significant cost associated with that in terms of development, manufacturing and support) that is relatively large and just going to sit there and take precious space on a pedal board w/out providing the user with any footswitches. It may be your goldilocks thing, but I think most people would think 'WTF?' You'd have to sell it as like a desktop recording solution or something, I would think ot get enough market appeal to even consider it...
It makes more sense to do what L6 did with the Stomp and provide as many switches as they could on pedlaboard friendly box and then let users add MIDI control if they need more. In fact they ended up adding more switches to keep people from having to f*** w/ MIDI on the XL.
So, you already have an option like the HX Stomp if you want something
tiny that fits on a pedal board and has MIDI, if you don't want switches ignore the ones that are there. :) The switches are not really costing you much on a unit like that and they broaden the appeal of the device to more customers.
For more capable hardware, the physical design requirements would quickly become a constraint if you want something that performs at the Full Helix/FM9/QC level... Seems like the DSP and I/O in a modern digital unit is going to require too much power, run too hot, have too much I/O and be too big/clunky to not have switches on the device to justify the size it is going to check in if it is going to marketed to the floor crowd... I would think the QC is about as small as you could go, so why NOT put footswitches on it at that point? They double as knobs anyway. Barring that you are back to rack units.
TL;DR: If there were a market for it and it justified the cost, L6 would have built one already. IMHO.