It's been quite a while since I watched an episode of Ping. It's good to have more technical people hosting Ping.
As for add-ons for the Surface it would be great to have a keyboard layed out like the Grantophone app. The advantage would be that it's pressure sensitive, unlike a touchscreen.
A Harpejji style keyboard or a hexagonal one like the AXIS 64.
Having the current one with the faders and the MPC style pads show up in any app as a standard MIDI controller would be great too.
It's pretty much useless without MIDI support.