You won't use it for the Hytbold gear (the pre-raid teal sets coming with RoR launch).
The instance cluster and its gear is still in the pipes, so nobody except Turbine employees and, just assuming, Palantir people have an answer for you. And they won't give you an answer at this time.
Nobody knows for sure at this point, so all we can do is guess. Turbine generally doesn't like people to save up currency in order to buy gear right away, and I understand why. However, it seems like they waste time and resources developing a new currency revamp with every expansion, so it's really hard to say what their plans are. After streamlining everything into marks, medallions, and seals with the Isengard Instance Cluster, it seems odd that only a year later the would scrap the system and go with something else. But, that's always a possibility.
I've said in the past that I wouldn't mind if they simply converted everyone's current seals into an equivalent number of medallions, and start everyone back at zero seals. That way the new instances could continue to offer seals, while the old level 75 instances could offer more medallions. In theory it sounds much simpler and less complicated than developing a new currency or adding another tier above seals, but you never can tell with the way Turbine operates.
~Landroval~ Raigar - 75 Captain | Raigorn - 75 Hunter Captains of the West - Leader
Founder | Lifetime Member | Raider | Roleplayer
Turbine generally doesn't like people to save up currency in order to buy gear right away, and I understand why.
Wouldn't surprise me if this is also why the ToO gear requires you to have completed various ToO deeds (which are completed by successfully running ToO runs). Won't surprise me if Turbine does the same thing for Rohan IC. That way, regardless of seals and medallions, you will have to run all the relevant raids/instances in order to get the gear. Which, in my experience, is not easy, especially when the IC just launches, because everyone will be learning how to run them. Even when running in groups with experience you can still encounter difficulties that can cause the raid to wipe or otherwise fail. My biggest hope for the Rohan IC is that it will not bug the way Draig is infamous for doing.