If Sony get the F1 licence again, then let PD make it based on GT6. Then make it so that if you own and have installed both GT6 and F1 20XX you can play the F1 game using the GT6 disk (in the same way add on packs work on a PC game).
Seeing as that's unlikely PD should add some classic F1 cars to the game. They have existing licences with Ferrari, McLaren, Honda, Toyota, Renault, Alfa Romeo, Mercedes, Ford, Jaguar and BMW and with various buy outs and takeovers, these manufacturers probably own the rights to many other F1 teams (e.g Mercedes GP-Brawn-Honda (who PD also have a licence with)-BAR-Tyrrel. Lotus-Renault-Benneton-Toleman.)
If this can't happen either, PD could add the F1 replica's from GT3 (a standard open cockpit like the FGT would suffice for these cars) or even get a licence for the BOSS GP series (Classic F1, Indycar, CART, GP2, F5000 etc all racing each other).