If anyone wants to help figure this one out....

It turns out that if I try to remount / read-write at preinit time, preinit goes into an endless loop of stack dumps that causes me to have to reinstall a stock kernel. I think that this is because it's just managed to remount it from the initrd root. I considered sleeping for a second or two, but I didn't want to delay startup, so I haven't even done it to check to see if that's the case yet.

But if anyone has any ideas, please let me know. The offending code is still in the source ifdef'd out.