Now, onto your IR BVR missile, well that sounds a lot like the IR MICA tbh, and apart from the French, no-one seems all that keen on the idea. The Americans, Russians, Chinese, even the British and Germans never seriously tried to come up with something in the same class even after all these years. That clearly shows a consensus.
I do not like long and verbose post that don't get to the point quickly.
I will reply the rest later.
but...
Almost EVERY ONE of Soviet Long Range AAMs had both an IR model and a SARH model. The standard soviet tactics seem to rely on salvo firing both too.
and they has had combat success too.
In gulf war I, an Iraqi Mig-25 firing an R-23T IR-Medium Range well beyond vis range score a kill on an American F-18.
They are not as impotent nor neglected as you think.
certainly Americans were aware the effectiveness of such arrangement. The fact that both entry for the replacement for Phoenix missile the AIM-152. AAAM, put an IR-sensor as the terminal seeker in their design.
and as you mentioned the French were interested MICA IR,
And are you aware that the IRIS-T has an 25 KM range, which was in beginning an requirement from Germans. So that crosses out Germans.
AND....
are you aware that the British led AIM-132 ASRAAM (or ass-ram) one requirement was to trade maneuverability for range, resulting most importantly much better kinetics at those range than the typical short range AAMs? based on a airframe that is not bigger and heavier than an standard AIM-9?
so out of that list...
The Americans, Russians, Chinese, even the British and Germans ...
That leaves... CHinese.
as the only ones do not have an good IR Mid range AAMs.