I see a problem with any „coaxial“ attempt in one horn. The length of the horn is correct for one band, but not both HF and MF. If the horn is optimized for MF, if is too long for HF and works like a transmission line at those frequencies. The wrong horn flare means that the horn EQ is applied to the wrong frequencies with no appreciable gain where we need it.
Is a point source a „worthy“ goal? What sonic advantage does it offer? Is there a problem with convergence of the MF, HF and UHF at the listeners seat or is it a myth to promote hifi agendas?
Horns are decade devices as a rule (with few exceptions). That is based on the geometry of the horn, not how wide band the driver is.