Could IR AAMs be launched from the main bay (at the expense of fewer radar guided AAMs)? ISTR on the F22 the AIM9X swings out on a trapeze so the seeker can get a track before launch.
They could, and with LOAL capability pretty much standard on all the newest IRAAMs, not having the seeker outside before launch isn’t a massive issue. Indeed, that’s how the F35 is potentially going to launch its own IRAAMs.
The real issue with using the main bay for IRAAMs is going to be the operating limits of the main bay doors, because those would have been designed for use at high altitudes with relatively straight and level flight in mind.
I would not be surprised if the main weapons bay doors of all current 5th gens will simply rip right off the airframe if they were opened at low altitude, while the jet was pulling 9G+ since they would not have been designed for that.
Maybe the F35 might be able to manage it due to the unique design of its main bays, but I would be amazed if the bays on the F22, J20 or J35 could survive that due to their design (assuming the J35 bay has not been radically changed from the FC31).
Even if you re-design and/or beef up the main weapons bay to be able to open safely during a dogfight, it will still be sub-optional as exemplified by the agonising ‘lag’ on the F22 between when the pilot presses the trigger and when the side bays finishes opening and the missile actually leaves the rail.
This is another reason why I love the J20 side bay designs so much, since it neatly sidesteps that issue and gives the J20 the best of both worlds and stealthy internal carriage and zero delay to launching the missiles.