I agree with @samueltardieu that the size of the DB is not the big deal, so we should keep it in the internal memory without any selection. AFAIR we discussed problems with missing DBs recently which might have been due to a removed or write-protected or full SD-card.
But I also agree with @rsudev that removing an existing feature will make this attempt quite complicated.
What happens currently if I deselect "DB on SD"? There is already a procedure to move it back, isn't it?