Exclusive, vanity-based rewards is the only way to go for something like this IMO. It would also mean those with full ilvl/BiS gear getting to put said gear to use during the current cycle in content that's designed for it. The initial problem with Savage Coil was it sharing the same lockout (and loot) as Second Coil, so it hindered any incentive for others to do it in fear of ruining their chances of getting loot. At the same time I wonder whether it's worth designing 4 more fights for the sake of a minority within an already minority group, but if Yoshi already has the viewpoint of 'If we do it, well don't complain about it being too hard!' then more power to them I suppose.