OMG, T-3 is the most disgusting, horrible domestic terminal I have seen in the US. Makes LGA look pleasant.
That said, there is a rationale to get the major carriers for each alliance co-located and complete post-security connectivity between T-3 and TBIT. What's interesting to me is how UA is sitting on their gates. They have not been in much of a growth mode and have slipped to #3 in pax traffic at LAX behind DL and AA (though all three are close to one another).
If DL moved to T-2/3 I would pray hard for replacement terminals worthy of a 21st century airport. If that is the case we're talking years (if not a decade) before DL would move.