Originally Posted by
goatalope
I'd have no problem riding that until a new wheel arrived.
+1, if it's a crack, it's probably a stress crack form excess interference in the bearings fit. Possibly someone rebuilt the hub, and cammed the baring pressing it in. In any case I doubt you just happen to have caught is as it was reaching the meatier part of the shell, sso it's probably been that way for a while (maybe a very long while).
There's not much reason for the crack to suddenly start extending, especially because there's lot's of meat in the shell under the flanges, and this is the left side where all stresses are just over half what they are on the right.
I'd ride it until I felt I had a reason not to or trashed the wheel, which I wouldn't rebuild on this shell.