2004 Honda CR-V, ~140k miles, overall good condition. Got tie rod ends, ball joints, and shocks replaced this summer so it's probably not any of those. The wobble showed up suddenly about a week ago and has come and gone since then--it only appears at highway speeds (>~60mph) though sometimes it will be slight and sometimes it will be dramatic and terrifying.
The car is in the shop right now, and the guy at the shop said it's likely to be a busted tire belt, which would mean replacing that tire. So I'm likely to find out what's happening by close of business today, but I want to put this question up to find out if there are any other potential causes, and also for posterity since I haven't found much else about this specific issue. Will update when I hear back from the shop.