Unfortunately squashing doesn't help as much as I'd hoped as the performance problem is in the loader (executing migrations is pretty quick). It can also get tricky with interdependencies between apps.

Turning off migrations is great in the cases it works, but it doesn't provide an easy way to also run the few data migrations that some parts of our code rely on. Obviously we could probably fix this in some non-DRY way, but I'd rather not.

The situation as is, is workable, but it would be way better to improve the performance of this a little (which I have a feeling is definitely possible). When I next get some time to work on this, I'll give it a crack.