So I've fiddled a bit more with this region, added an extra mountain chain running through the middle of the map, an extra island, tweaking some of the edges. This seems to turn into a great region, still needs some more tweaking here and there.
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I've made this gif to show the difference between version 1 and version 2. Nothing much besides the mountains and the added island.
Click for larger image (1,7 MB)
I think the level of flatness is good now, Stil want the downtown area(s) to be in a flat environment, or add the hills in mayor mode.