Looks great!
To give an example of some useage of this map: here's a vague sketch at a theoretical Byzantine three-zone AOR. I don't know if there's plans to introduce AOR into SSHIP, but this could be food for thought in any case.
Dark purple: "Homeland" region, full range of factional troops.
Paler purple: "Expansion" region, factional troops limited to "professionals" and elite troops, to represent assimilated elites and locals fighting as part of imperial armies. Note, these are troops only available from higher tier barracks, representing the time taken to assimilate a region.
Palest purple: "Conquest" region, factional troops limited to elites, to represent small pools of assimilated elites, and a population very distinct from the imperial centre. Again, recruitment is limited by the need to build only higher tier barracks, which will only yield very limited, albeit high quality, troops.