I've heard elsewhere in a podcast that Harman expect to have the next iteration of Phoenix out in under a year. They seem to be very confident of making rapid progress towards the goal of a normal, everyday colour film.
It's pretty plausible that at the point that Phoenix II needed to be cleared to go for wide coating (or risk missing the available coating window) the yellow masking dye (to take the obvious example) was very close to being ready for incorporation. Once it's incorporated (and any undercuts that will impact the red/ cyan layer), that'll be the point at which anti-halation can be done (as they'll have a more final answer for overall emulsion internal behaviour etc). Once you have a known & good set of couplers and masking couplers, refining the emulsion characteristics (especially in terms of grain/ speed etc) elsewhere becomes much more achievable. I do wonder what the final speed of Phoenix III will be (I'd guess the aim is 200, but I suspect that it might have to be 100 initially).
There's an acknowledgement on Harman's part that a number of customers want more sheet film and it is under consideration.
It may well be that instead of making a new poly-base sheet only version, Harman decides to move a particular (relatively minority market, let's be frank) emulsion over to poly base completely. If they were to bin Pan-F and replace it with Delta 25 on poly base across all formats, I would not complain.
As for 900nm sensitised film, I do not know how difficult that is but I would imagine that if it were cost effective, someone would be producing it. If it were a quick tweak of SFX, Ilford would be making it.
Long story short, it seems to be to do with the limited longevity of the sensitisers (and general fogging from the environment) relative to the volume of sales per annum. I suspect the price per roll would need to be higher than Ektachrome and the expiry would be less than a year from coating - both would be more manageable if there were other markets that bought very substantial amounts for governmental/ industrial purposes (as was the reality in the past).
I would assume with all the technical know-how out there, yet they end up with the crazy spectral plots for Phoenix.
What you are stating here is that you have limited understanding about how a colour neg film works in terms of its construction. Harman are working so as to minimise their need to completely restart from zero with each generation. Phoenix II's oddities are because it has been designed to enable the rest of the masking dyes to slot in (with relative ease) which will shove the curves into the correct relationships. They know the aims and how to get there, but the challenge is making quite complex dyes that need to work well on a reliable basis and can be manufactured efficiently and cost-effectively.