All quakes trace AABB vs AABB just fine. XReal didn't need to add that. They were probably refering to something else. Quakes can trace AABB vs AABB, AABB vs Brush, and AABB vs unaligned BB (tho this is disabled in all of them). They can't trace brush vs brush, nor brush vs AABB, nor unaligned vs brush, nor unaligned vs AABB. In short, the object you move has to be always an AABB, and the object that receives the impact can be of any of the available types. Quake 3 also adds capsule to the mix, but also disabled, dunno if it's functional.
A fine solution for the problem you describe (without modifying the collision code) is splitting the movement box and the hit box. That way the movement box (object that moves) remains always axis aligned, while the hitbox (object that receives the impacts from weapons) can be of any type, be it AA, a cyllindrical brushmodel, unaligned, or even a bunch of unaligneds tied to the model skeleton. This is what they did in HL (1) to implement skeletal hit detection.
