The idea of a new high-level city in the WZ is very cool, but it may be very hard to implement in the game as it is. I think that enabling bonuses for holding forts it's a shorter way to improve gameplay (working like a passive skill, for ex. the realm that holds samal wins 5% of bludgeoning protection or something better... I don't address balance issues but a nuke to hunters at lvl 50).
The invasion of the inner realms could make sense if it worked like a timed quest, say "kill all towncriers of the realm in 30 min", that could be multiple (add "kill all Flyingspears in 30 min" for ex. or similar as long as it worked with the lore story) so that there was some motivation for some time (then it could be renewed), after the quest time limit the invaders would perish in some strange and disturbing way (in Ignis they would suffer from instant combustion, in Alsius they would freeze, and in Syrtis they would win some fairy wings while the latest Barbie hit plays and eventually they would disappear in boredom) respawning at some of their realm beacons. This way we can assure noobs protection (no RP for below lvl 30 kills) as we add an objective to invasion (and Znurre can do some sightseeing for some time).
Also it could be added some kind of monument for each invasion in a very requested place, like arround Samal, so that we can brag about Ignis being the best realm in Regnum.
I have some more ideas but i should keep them so that I can use them in the next job interview...