As much as I know this bug severely hamstrings you guys in what you're doing, you have an acceptable workaround.
The one bug that, IMO, is far more insidious and has NO ACCEPTABLE WORKAROUND, affects you guys just as much, perhaps more, than the specific issue. Navmeshes. Even if all the noise yo make gets someone's attention on the dev team and they fix it, you guys need to navmesh all of your new material and once you realize how insidious THAT bug is, all of your efforts will have been entirely wasted.
None of your outdoor cells would work. None of your interiors. None of your caves, dungeons, and other stuff. Nothing. Converting your file into an ESM will not work to correct it. The game will simply ignore the changes instead and all your connective tissue between vanilla Tamriel and the expanded areas will be non-functional at the connection points.
So while I get the fact that you guys want this -64 thing fixed, it really would be of far greater benefit to everyone to concentrate the attention on the bug that affects the entire community across the board.
There is no good reason why we cannot ask Bethesda to fix both so we need to combine our efforts rather than divide into two camps. Without Navmesh, no large worldspaces, without large worldspaces Navmesh potential and usefulness is much, much less.
So with one voice we should be pushing for a patch:
Please fix
Worldspace bug, navmeshes, LOD generation.