I havent tried it yet but this one sounds good: http://www.twcenter.net/forums/showthread.php?t=245384

Also the idea of having only some certain regions to be able to build up to a certain level is cool. Although it needs a lot of thinking it through, as it may cause huge balance issues (which ones ). I belive the "smallest" regions could be build up to castle/stone wall level.
I also like the idea of capitals having more value (they could be getting some additional money for it (e.g. depending of the level of city/castle walls), or bonus happyness for splendour of living in the capital, or that you would be able to recruit some extra unit like Palace guards or something) Which would of course have to go away when you switch capitals. Maybe it could be done with an additional building that gives those bonuses and is automaticly destroyed when you change capitals and buid (also automaticly) the next turn in the new capital.

And the stone forts that are destroyed after some time of being unoccupied is nice.

Oh and are those ideas only for the next RR/RC or for the next release of this great compilation of mods: REAL RECRUITMENT 1.3 / REAL COMBAT 1.8 for STAINLESS STEEL 6.1 BETA ?