One subtle but important note: datadir is actually where Armory data, such as config files and wallets, are found. By default, within that directory is a "databases" subfolder, which is where the Armory DB will be found. As written, I don't think it's easy to override the DB location. ArmoryDB can override this setting in armorydb.conf with the "dbdir" setting, as seen here. However, command line invocations, such as the one Armory uses, override whatever's in the config. So, Armory users would have to alter the code to either not use dbdir in the command line invocation, or alter it to use whatever it is they really want.

(All this will be placed in an ArmoryDB README. Pinky swear. It's almost done. I've just been distracted by more pressing matters.)