You see zOMG bundles there forever on the Cash Shop. zOMG has been nearly all but abandoned by devs considering how it's been in beta since day one. I think it's safe to assume countless people have spent tons of GC on zOMG Bundles, so why not MG?
Users could spend x amount of gc for a blue coffee or a bundle of 10 or a super bundle of 20, like wise for Star seeds (Like in the iOS MG: Zodiac Islands only GC) not to mention a mega pack of 10 Coffees and Seeds or 20. I'm certain that would easily be a major seller and gaians would be happy for sure (So long as prices are fair naturally.) It's almost impossible to see any downside from this no?