It's a tricky question & although I am not in the position do give a definite answer about NetApp plans, I don't think it will be supported in the nearest future.
Bear in mind FC is used in MetroCluster support for back-end, controller to disk shelf cabling & that's something very different from host connectivity. In particular there are no disk drives / shelves using FCoE.
FC disk drives though eventually will be all replaced with SAS drives. So for me the more intriguing question is:
when will we see SAS-to-FC (or SAS-to-FCoE) bridge to enable DS4243 shelf support in a MetroCluster setup?