The thread I made discusses the possibility of creating a script for actors as well... I'm not sure how well that would work in the case of full blown wars, not even sure the idea is doable at all... but it is an idea to discuss.
I sincerely, fervently, hope that there is eventually a fix for this problem... hack/work arounds/pie-in-the-sky wonky solutions should not be required to begin with.... and I really would like to see MERP and Mes and a full Tamriel in their full, non-split up glory!
Sadly, for now, we have exactly 2 options until/if a fix can be found: 1) Put on hold/don't do large world spaces 2) Break them up, come up with some other hack/workaround.
The issue is not making a script that teleports actors, the issue is making actors use them properly like the world is seamless. It's not impossible but just an insane pain and time consuming.
We do have a third option, and that is developing in the safe zone which buys us a lot of time to find a fix/workaround, without losing any valuable development time. If there's one thing I learnt from MERP in Oblivion, then it's that a big total conversion cannot afford being put on hold. You need every single month of the youth of the game. Speed is most important, it's the difference between the project dying a slow death or actually finishing it. Accommodating for the supportive workarounds (like the teleport script) that would be required when splitting up will consume so much time when actually developing content... That step should only be taken if a death of the project is otherwise guaranteed.