Do you have any detail on this? Anecdote: My 4 years old gates belt drive mid-motor ebike with nuvinci has passed 14 000 km now, with no sign of belt damage/wear, and no cleaning done. Ridden year round in sun/rain/snow. I don't know how long it will last, but even if it suddenly snaps tomorrow I'll be happy with it.

Maybe true for most of the riders that use belts. But for a strong enough rider, belts are more efficient than chains. I don't recall the exact wattage point where the belt wins, but it's been measured thoroughly. Of course in muddy/dusty MTB use, or with poorly maintained rusty chains, belts can win even with quite low wattage, I'm sure. Belts are an excellent option for the right uses.

For the Birdy, yes, because of the slanted pivot axle and the folding limitations. But variable chainstay length and belt tensioning in general is no longer a dealbreaker with belts, several manufacturers make such bikes now including R&M.

This is no longer true, I think. For sure the NuVinci / Enviolo can shift with power (though I would only recommend this hub for ebikes because of its low efficiency). And there are several new-ish options now like the Kindernay and the 3x3, made for MTB and/or ebike use. Are we sure those can't be shifted with power?

Anyway this shift-with-power thing is overrated, I think. With derailers it accellerates cassette/chain wear, so there's a benefit to reducing power anyway. Those who haven't tried IHG's may think the issue slows down shifting, but I'd say that's not generally the case. My Alfine 11 shifts instantly, always, and I don't have to stop pedaling, just reduce pedal speed. With derailers the shift speed depends on how fast the wheel/cranks are rotating. If climbing a tough hill in the 2nd lowest gear and I need to shift down, that shift can be very slow, while at high speed the shift is quick. (I ride with chains, belts, derailers, Alfine 11, Nuvinci, and Sturmey-Archer 5-speed. Each of those systems are excellent for their uses.)