Air forces like commonality so I’d imagine that the front runner would be some sort of Hawk, given the Hawk T.2 is used to train RAF pilots. Perhaps an austere version of the T.2 will be developed, which doesn’t include all the expensive electronics required to training pilots to fly Typhoons and Lightning IIs but which shares the airframe, engine and as much else as possible with the regular T.2?
Alternatively more and more air forces are using turboprop aircraft for their display teams so perhaps the Red Arrows will do the same. The RAF’s Tucanos are being replaced with Beechcraft T-6 Texan IIs so perhaps they’ll get a few for the Reds as well as for pilot instruction?