Once Followers rank up to Epic, Follower XP becomes entirely useless. This wouldn't be a problem if it weren't for the fact that the majority of missions reward follower XP (even at 100, with stuff like 15,000 XP missions). It feels like a massive waste to just send epic followers on those missions and not get anything in return.
Which is why I think Follower XP should translate into something else when the Follower is Epic.
One possibility I was thinking of is that when an Epic follower gets XP, it goes towards a "reroll" of one skill. So for example if a follower gets enough XP, they can choose one of their counters/traits and change it to something else. To prevent people from obtaining 25 followers with Epic Mount/Scavenger, they could make it so the process is random, and you're just rerolling for the possibility of something different.
This would also solve the issue with having a whole bunch of followers with the exact same counter. I'm have 9 followers with Minion Swarm counter, and it honestly feels like every time I upgrade a follower I get the damn Minion Swarm counter. This solution would allow me to reroll that counter for something different.
And yes, we do have the "follower reroll" item, but I don't think that's enough. The mission is incredibly rare and since it rerolls everything, it can end up doing more harm than good. Just today I rerolled one of my followers and got the exact same counters, despite the entire point of me rerolling it was to get rid of those counters (yes, minion swarm was one of them).
Overall, this idea would allow us to min/max our followers better, and would generally be more rewarding. But does anyone have any other suggestions?