Price point and size. I believe that is the winning combo.
As for what do you remove? Well, you have to give up something to make it smaller. My suggestions were to get rid of one of the 4 efx toggle buttons, move the tap tempo up to the top and shrink the FC form factor down by 4" making it around 12" long, and the same height as today's FC.
Only WiFi editing.
I totally agree with others that the engine needs to be completely left in tact. No sonic downgrade for sure.
I am even suggesting that the full 5 performance slots be accessible from the controller as well as the up down performance buttons, just none of the stages controller features. Those would all be done from a tablet.
So what you cut is lots of buttons and knobs and a couple foot switches.
$1000 seems like a pretty good target price for me.
Kemper rack or toaster with FC ~$2400
Kemper Stage $1700 (41%)
Kemper Mini $1000 (70%)
They could also go with the hobbled FM3 approach to keep the Mini from cutting into the stage market. Just 3 or 4 buttons and the current LCD. That would justify the precipitous price drop from the stage.