Just in case anyone is still habitually using a USB mouse... I tried using my own fix earlier this week to find the first directory didn't exist. Turns out, the trackpad now works in Arch, and it responds and behaves better than in the previous solution.
It had been a while since I'd tried using it (habitual USB mouse use), so I can't say which update did it, but if it hasn't propagated to other distros I would expect it to soon.