I wouldn't even call it a loophole. It's totally legal. Trusts are stated nowhere in 922(o). The form 1s for MGs being submitted currently are being disapproved right now, but people are still submitting them to gain representation for an upcoming lawsuit. With any luck, the FOPA and NFA house of cards will burn. Any changes to the current laws require an act of congress, so if the courts decide in our favor (in the same manner as Heller), you're going to see a ton of new full auto trigger packs and whatnot for AR-15s, and who knows what else.

edit: well, that's at least before the congress critters draft up something idiotic.