It won't be released until it's ready.
Gingerbread on the Thunderbolt won't be anything like Gingerbread on the Nexus S or Nexus 1. It'll have Sense on top of it. It'll be different. It'll have its own problems, just like any other update for any other phone does.
I'm running a port of a gingerbread sense ROM now on my myTouch 4G and so far it's pretty darn good. It's only been a day so I can't comment too much, but if they spend as much time on Gingerbread for the Thunderbolt you guys will be happy.