i'm going to try it. it doesn't work if you try to do it via a terminal emulator, but hopefully it'll work when i do it via the PC.
IO speeds are def slower (i have a 95/90 card) but for the trivial amount of data being accessed i don't see it being an issue on a daily basis.
plus you can still manage what is stored where iirc, so if there are apps you need to have stored on internal for the most extreme speed, then you can do that.
i had gotten mine down to about 7gb free and then uninstalled some stuff. but mostly the 64gb card i have had like 80mb used before then so it just seemed like a waste to have it sitting there while i fill up my internal storage.