be stupid to use the 2.8 when a 3.0L turbo would be better.... cheaper in the long run?
I don't know about "cheaper". There is no reason to believe that the 3.0 DI Bi-turbo will be cheaper than the 2.8 port injected engine with a single turbo. The problem is that the 2.8 is a surgy powerplant that is problematic in service. Cheaper or not, the 2.8 has to go.
The 3.0 is probably going to be between 300 and 360 hp. To maximize its potential, it'll need a new automatic transmission with a greater torque rating than the 6T75 (300 lb-ft). Without it, the 3.0TT will be pretty close to the new LFX 3.6 in output (318~323 hp / 275~278 lb-ft). Yes, it'll have a flatter torque curve and maybe 20~25 lb-ft more twist, but that's a slim difference to try to sell the extra cost, weight and maintenance worries of a pair of turbos and a myriad of IC plumbing on.