JetBlue who? The airline that's making profits this year, unlike United, and which offers low fares instead of trying to prop up an untenable cost structure.
Still, I doubt B6 would go after DCA-LGB because it would cannibalize their flights at IAD. It's unlikely that B6 would abandon IAD for DCA because the transcon slots at DCA are so few. JetBlue, I think, wants to grow transcons in the DC area, and Dulles allows them to do that.
I agree, anyone but US or UA should get the DCA transcon slots. Too bad America West wouldn't run DCA-LAX; they'd offer lower fares and stimulate traffic on a valuable business route.