Just to bring this a little into perspective: The feature 'db on sdcard' was implemented around two years ago (#1555) and at that time referred almost exclusively to an external sdcard (the current seemingly ubiquitous internal external ones not very widespread back then). I can't remember a single support request due to somebody removing his sdcard and falling back to internal storage for the db, but many people appreciating the possibility to lift the pressure on (true) internal memory.
So if we would really want to remove that feature, we also would have to have a migration procedure and some idea how to handle the case that the (true) internal memory is not large enough to take the db back...