It should. In some systems (like unpatched windows xp on 32 bits), some size limitation occurs naturally. It's because the system addresses memory using 32 bit locations (i.e. if the system wants to look at location X in memory, X must be a number that can fit in 32 bits). Now 32 bits can only hold a number that corresponds to 4 GB, so that's why you can't use more than 4GB of ram on xp.
48 GB is a rather arbitrary number, so if the card can add more than 16 GB, it should work. Also, the kernel is linux, which can use humongous amounts of storage.
Note however that i haven't used maemo, so i can't guarantee there isn't some some quirk. Unless some maemo authority says otherwise, it should be possible