I'm incline to think they should cut tomestones/Wolf Marks out of (ranked) Feast and have them solely for Frontlines. Anyone queuing for Feast is queuing for rating, the other rewards are nice, but they mean Frontlines is essentially worthless... I suppose you could just add some new currency style reward to Frontlines to draw interest to it, but that seems like too much effort. All we need then is a solid purpose for Wolf Marks... Then you have a situation where Frontlines is constantly active as people need Wolf Marks, while Feast loses some activity for a time, but hopefully a stronger and consistent casual scene allows the competitive scene to grow in the long run.
I'm not sure what to do with Wolf Marks though... Materia would be very nice, but completely irrelevant to PvP... With Frontlines being the casual scene though, a PvE reward like that would definitely help... What we need is a reason for people in the competitive scene to need Wolf Marks and thus ensure Frontlines is fairly stable... I've seen a few people suggest cutting out Limit Breaks in favor of a more specific "Job ultimate" skills, and I think something like that could work really well if we making it similar to the Heart of the Specialist skill... So you'd have an ultimate PvP ability, but it uses up a consumable that you obtain through Wolf Marks... Could have alterations on that concept, you could perhaps use the skill no matter what, but the consumable effectively gives it full potency, something like that... Unlike PvE rewards, that would be something PvPers would definitely go out of their way to obtain, and as a consumable it'll provide a constant purpose for Wolf Marks.
Can also work it with Frontlines just being far better than Wolves' Den for farming Wolf Marks, perhaps having that 600 Wolf Mark bonus from the Roulette be a "In need" bonus, rather than daily one... That would also (hopefully) provide variation in Frontlines, as Seize would be just as viable as Shatter, and if they ever decide to give us Lv60 Secure/Slaughter, even better...