HTPC Guides has a fun post detailing how you can make the Banana Pi (and presumably the Banana Pro) work with multiple SATA drives. Using a SATA multiplier from AliExpress and a 2.5″ HDD enclosure with separate SATA ports more drives can be hooked up.

At the time of writing, a minor change and recompile of the kernel is required. However, if this catches on, it is sure to be supported out of the box.