Because I stupidly forget that something as stupid as a touchbar was created in the first place. Perhaps it'll be the Air in that case.
Edit: worth noting that the Air is more likely to thermal throttle the Pro, which would be a major reason to go for the Pro. I support it'll be alright if it's mostly connected to a keyboard.
Go with the Air. It's not a huge difference in thermal performance as far as I can tell.
We're going to support the Touch Bar to make those machines useful, but given it's likely to be dead in the next generation, it's unlikely Linux will get any kind of ecosystem for it unless someone is really dedicated. I can only promise basic function key emulation (same kind of thing you get on T2 Macs with Windows/Linux), and it will take some time since that needs a couple bespoke drivers and we have bigger fish to fry first.
Then again, you could also wait for the next generation. As long as M1X didn't redo the GPU, which seems unlikely, I don't expect support for that chip to lag much behind M1.
My feeling has been that linux on M1 isn't going to be stable until the next generation so I was definitely going to wait. But that's future talk. If it becomes stable, I may just do it.
Rumors are that the touchbar is going away with the next generation of MBP anyways, so it may not matter.
As for thermal throttle on the Air, you can spend $10 and 10 minutes installing thermal pads to bridge the CPU and the aluminum backplate. This will cause the backplate to heat up more, but nearly eliminates any thermal throttling even under sustained load.
Edit: worth noting that the Air is more likely to thermal throttle the Pro, which would be a major reason to go for the Pro. I support it'll be alright if it's mostly connected to a keyboard.