I do not know. I always thought the there are at least a couple of ways to improve on the head unit was to hack it to allow side loading of other apps. Or, to find a better modern unit (basically whatever unit is in the Elva) and write an app to be backward compatible with the CAN other stuff on older models of IRIS. Also, I bet some of the older apps (like climate control apps) might run unmodified on the newer units.
I think the problem is, unless we get a really technically competent individual with a lot of energy and will to focus on this, the market just is not big enough for anyone to put in the work for these outcomes.
Of course the best positioned company to do such things is McLaren itself, but they seem uninterested. Shame, they probably could make the new elva head unit available for older models with not too much work, and they probably could charge $5k to upgrade it. Sadly, McLaren pricing on development seems on the order of American aerospace defense contractor pricing for development, where hammers cost $10,000. Also, I suspect there is zero desire to upgrade their really great cars and they hope that motivates people to upgrade to new models.
Would love to be wrong.