Purely for the sake of thinking and discussion:
How well would it work out to take a big chunk out of Atamara (or other island - they are mostly modeled from same template) that would be the right noble density, but with (for example) 8 cities each hosting a realm, and then play everything else exactly like the War Island is set up now?
8 might be too high, but there were approximately 240 nobles on SI when it started - so 6-8 might fit.
That's it - discuss!