Could it be that Roland merely included SRJV expansion slots in the XV synths to entice JV/XP owners to sell their synths and upgrade to XVs? I reckon Roland would advise you that you could get some great guitar sounds by selling your XP-60 and buying an XV-88/5080 (or, better yet, you might want to keep your XP for the sequencer AND upgrade to an XV-88/5080) and loading guitar samples.

Your option "a" sounds reasonable, though.