Air-to-air capability would most likely come as the side-effect of a radar replacement. By side-effect, I mean a radar that offered tactical advantages in the BUFF's normal role... but the software of the radar offered other capabilities.
Of course, it's not just the radar; you have to trial flight the weapons config, do ejection tests, launch tests, verify the flight envelope with captive carriage, test missile exhaust gas impinging on the turbine engines, reprogram the weapons computers, train crews and finally reach IOC.
To do on an airframe that is in a "let's keep it as long as we can" phase makes no sense. If the USAF committed to maintaining BUFF's until 2050 with a major upgrade... then things get interesting. I doubt we would see an AAM capability unless the world situation changed drastically. A "latent" capability perhaps, but a real honest-to-God capability... big doubts.
Interesting that the pylons are still in use though. They could see use with some of the small, low collateral damage, missiles now being fielded. That would give the BUFF a flexible response capability to pop-up targets.