Unfortunately it's too late to join GCAP. Germany has everything to build an aircraft on her own, except an engine. The easiest way would be to license produce the GCAP engine and integrate it in a new fighter. Luftwaffe wants a big aircraft.
Well, they still have EJ2000 itself, and MTU still exists. Up to debate if MTU is truly up to the task to design an engine by themselves, but they do indeed have money to throw at problems, and their starting position is certainly better than Korean/Turkish ones.
Furthermore, as China recently shown, one may want aircraft, or they want to make excuses.
Even with EJ200(230/270?)
3-4 engines aren't best, they aren't somehow legally prohibited either.
Alternatively, idea to build their bespoke Ural bomber can be shelved, and they may do away with a more moderately sized aircraft.