Sure, I'll take that list...
I will be away for the first week of September, but after that I can spend some time on this, and with the emulator it will go a lot faster as well.

And yes, there is no good way to solve this without doing it properly. Or at least it's not worth it.
Just need to for example half the boost resolution precision... and adjust everything that references boost.

Also, it makes sense to do this on 551K, but not so much sense on M-box, etc. This is because if your load axes cap out at 191 on crucial maps you can't really tune properly anyway.
So you might as well underscale...

how do 1.6++ bar engine mods work with ME7 properly without dirty hacks?

so the big picture "project" will be modifying the ECU that it work like stock and proper diagnostic, internal physics:

- underscale MAP, PU and all 16 bit pressure values by factor 2, find all references in calculation, maps, curves, values in parameter space and shift accordingly.
  Underscaled 16 bit should be still precise enough: better than 0.1 mbar

what about 8 bit occurrences?

do any stock ME7 exist with controlled boost over 1.55bar?

They don't right now.
You underscale the MAF to keep LOAD sane, and used fixed DC in the last row of the duty map...
It works more or less OK, but of course spoolup could be improved by properly using the PID and underscaling LOAD takes a while to dial in, even if you only do it up top.

That said - on ECU's where all the load axes on maps like KFZW/KFZW2 are 8 bit, you will have to underscale load anyway on big power setups, because otherwise you can not control ignition over 191 load.
You can not solve the MAP limit without the LOAD limit though and vice versa, because these are connected.