OK, I've got one of those Hungarian 72w/120v (100w=) GE halogen bulbs about to go boom I think:

It's all of a sudden today about as bright as a 29w.  When turned off, the halogen capsule glows like an HID lamp would! I suspect the filament is touching the glass.  Should I be worried about boom type consequences?  To be fair, it's in a drop/trouble light, which is like the worst place possible for one of these (the box even says not to use in vibrating or unstable places). 

Anyone ever seen this failure mode? How long might it have left?

If you see it in a weird state, better stop using that lamp.
In theory it should fail in a safe manner (that is what the code says), but better to not try your luck there. Because the same theory says ir should work normally until the filament breaks. And clearly it is not.