Does anyone have any thoughts on whether to get the new MBA, the 13" MBP, or wait for a more capable 16" MBP next year? I suspect the Air will be good enough to run Pianoteq. But the fact that it's running without active cooling makes me think prolonged practice sessions--or running multiple AUs and effects--might be too much for it.

Really depends on what you want to do with it. Indeed, for Pianoteq, the M1 Air is more than you’ll ever need. I wouldn’t worry about its passive cooling either, unless you want to run large sample libraries or synths like u-he Diva. In that case I’d wait for the upcoming 14” or 16”.