We've discussed the possibilty of a MOTUC Castle Grayskull playset, as well as Snake Mountain, etc...
Well, who would like a Prison Star playset?
If you recall, Prison Star was mentioned in a number of "pre-Filmation" era stories, about an intergalactic station where captured villains were held.
There is a great story in the first UK annual about breaking Faker out of the prison.
I think it would make a great little playset, and the "cells" could be great display capsules for the figures.
It could be really good.