That'd work really well. Make Two or three primium wards that are cash players only. Charge maybe 20% less gil as compensation, and then should their subscription expier even for one day their plot is vacated, all their non-moveable items destroyed, the rest of their items sent to an NPC, and all of their hard earned gil wasted.

And since usage of said primium plot would link your player ID to that area via the Mog Station due to the subscription based access RMTing gil for those useres would be impossible.