The 80376 was replaced by the 80386EX, which still kept the static core capable uf running at low clock speeds all the way down to halt to save power. But it also kept the 26-bit addressing, so wouldn't be appropriate for re-implementing at a smaller process size without a major update. But I do think it is probably a shrunken older core. I chose the P54C because it has already been worked on for the Single-chip Cloud Computer project and Larrabee.
Considering the only requirements we know from the article was "to offer a remote maintenance capability with high security." it's rather far fetched to claim a "poor technical decision" as you maintain. There are lots of reasons, besides the level of security provided, which would come into play in the decision by Daikin; think ease of use, maintainability, support, etc.
Using your reference design for a tablet with military grade security is not revalent as this is not a tablet, not needing to meet military anything, and only "high security."
And, no, I'm not associated with Intel, Freescale, ARM, or anyone else; I'm a retired engineer with well over thirty years experience designing embedded systems.