There is no need for more displacement.
I seriously doubt that HCI will be the mods for it,
and the "5.0" mentality era UD pulleys won't either.
The mods will start after someone cracks the PCM code for valve timing.
Chances are, Ford has already maximized the airflow in and out
(exhaust manifolds and system, intake, CAI) so there will not be much there.
Big gains from small mods, those days are gone.
I disagree on the displacement comment. By your own comments below that one you justify my opinion. The new 5.0 is going to be maximized out of the factory. By pulling big naturally aspirated horsepower out of a small cubic inch motor from the factory (especially high compression with good breathing), there is very little room for improvement. IE I go back to my displacement comment. A bigger block with more cubic inches has more room to grow.
Leaving the 5.0 in the GT is fine as long as they provide the 6.2 in the Cobra versions of the car.