A couple weeks ago, comex tweeted that a more efficient userland untethered jailbreak would be made available for iOS 4.2.1 before Christmas. But it appears, according to a @comex latest tweet...that it may be a couple days later.
MuscleNerd of the iPhone Dev-Team has a confirmed an untethered jailbreak working on iOS 4.2.1 firmware, this is essentially a back-up plan for the comex extensible jailbreak. The method MuscleNerd was referring to uses iOS 4.2b3 SHSH blobs which Cydia was saving for iOS devices in November.
Hopefully comex won't have to worry about the p0sixninja and MuscleNerd bickering over the SHAtter exploit being leaked, maybe he can put an end to it...
So I guess the word is..."give us a couple days" for right now. I guess comex will definitely deliver 300+ days before next Christmas!