This would be INSANELY Op, Considering there are only a few people that could even get to citizen to be able to silk the spawners, Its a no support from me sorry.
They had it on Factions and I think OP Factions. It's been removed on Facs now though, and to be honest I can see what you mean by that, since people like UncleUrnesto found a way to afk mobs before restart and get McMMO from them, so I guess it would be better to not be implemented. Although, I think they should have a /shop where you can buy spawners for a pretty high price, or at least pig, cow, sheep, horse, chicken, wolf, mooshroom, spider, zombie, skeleton.
I agree with Kinsey that the hole idea will be too overpowered, for example grinding out McMMO. No Support.