Neat! I love that H7 chip and its gargantuan inatruction manual... ...and you didn't even mention its 2nd core :)
Would not surprise me if the M4 was there and fused off (i.e. same die as multicore H7 offerings), but it's not active.
Do you know if it's fabbed in house, TSMC, or Samsung? I've seen ST silicon from all 3 foundries but the only thing I've seen stated publicly is 40nm. When I get it opened up it should be easy to tell, TSMC and Samsung processes have distinctive features on them that I recognize by sight.
Now this would be a cool blog post!