Maybe the Studiologic SL73 Studio would fit the bill, if you don't need sounds onboard (and whenever it actually becomes available)
Agreed - although I'm still nervous about that TP100 action in the SL73. Its predecessor the Acuna looked perfect on paper, but had such a horrible action I had to return it. I wanted to love that board, but I couldn't make it happen.
Yes, I have the same concern, and nowhere to try to SL88 or SL73 (when it's available). I'm considering the same type of arrangement as you, except (currently) with an Electro instead of a Stage. Thus, the P121 caught my attention too, until the lack of 5-pin MIDI.