openmw.org

To be able to have overlapping cells, for example two locations of a different time like Prince of Persia, allowing for seamless travel between the two cells via interactable "doors", spells or "portals", it could be interesting with Oblivion and the overworld but with them being topographically different, it would be difficult. I don't know if this is already possible with Caching, but that still requires loading, just less.