Presently only Eveline crystals have a use post-50. The remainder of the followers have no crystal usage post-50 and their crystals are thus dead currency.
These crystals are still rewarded for content. Is this a bug or a feature? I know 1.3 is the follower rework, so perhaps they will have a future use? See attached screenshots:
Hey!
We are still developing more in-game features, such as further uses for Follower Crystals! Currently, this is not a bug though.
The Follower update has been removed from 1.2 in our updated Roadmap as part of our June Community update, just in case it was missed 
As mentioned above, the Follower update will be coming with an update later in the year. Once the roadmap is updated again, we will share it in another Community Blog!
Jeto (she/they) - Support Human 
