Everyone sees 4 long range air to air missiles. That's fine. But I also see at least 2 air to ground missiles as an option. Or how about antiship misiles.
How are you going to hold them?
There are just this many suspension points inside.
Aircraft is supposed not just to support them, but to be able to freely maneuver with internal payloads. You can't attach new points at will, nor freely swap them. Also, the very same points can't be too small - for they aren't just to hold payload in place, their duty is to safely detach them from the aircraft, even under pressing conditions(negative/positive, off-axis overload).
I really suspect what this was a major reason behind su-57 design solution(and not lack of forum-level physycians in the russian academy of sciences): as flat as it is, whole height of the aircraft body below frames is availible for weapons bay, like in the bombers(just compare su-57 belly with tu-160, the similarity is striking).
J-20/F-22/J-31 have airducts, avionics and fuel over the bays. It doesn't matter for a2a(it is even good, because it's much simpler to use this volume with mraams = possible 6 missile loadouts). Remember the fate of the widow - Nortrop tried to be smart and lost.
This doesn't mean what this is the end. Just what a2g was a secondary concern, not important enough to sacrifice anything else.
