Great, thanks for that. Handling MIDI Clock/MTC is on the roadmap but it's going to take a few months.
You might want to consider routing from iPad via Wifi to S90 using "Live Routings." The latency is negligible (normally) and you could tell, say, Ableton what tempo you want from MIDI Designer. This is a bit kludgey and might be annoying. Depends on how much you want to geek, if that makes sense...