I was dumb and rebooted without redoing the kernel install, otherwise I probably could have just rolled back and reran mkinit to get fixed but the bootloader entry had already been removed for the old kernel as I think I was also running some cleanup commands, and when I booted to reduced mode I had no network to try and recover so I just decided to reinstall. Helps having a separate drive for files. Didn't have to worry about a backup or anything so it went smooth

It was an Arch-wide thing, there was an announcement on their site about it.