They should make a game that is the finale for both Wolfenstein and DOOM

It's revealed that the big boss of hell is actually Satan / Adolf who is the same entity, and B.J. Blazkowitz and Doom Slayer join forces to put an end to him once and for all. My actual theory is that Doom takes placein the TNO timeline, and the UAC is the succesor to the Party.

Tie in Commander Keen, as well.

All of the doom-slaying has weakened Hell's existing leadership enough for Adolf to stage a coup and take over. He reorganizes all the demons into a new "Eternal Reich" with appropriate style and symbolism.

Then BJ shows up as a ghost who fuses with the Doom Slayer in a Shadow of Mordor-type scenario, where you blur between their separate skill trees as you destroy Hell and the Reich for the final time.