I think there's some interesting space in martial support options. Though I don't know that any of it is currently unexplored. The only issue is that it's spread a bit too thin over all the martial classes/subclasses.
We have fear, disarming, forced movement, advantage, disadvantage, allied movement, temp hp, attack me or face disadvantage (essentially 4e style marking), even attack granting.
I don't believe at will action granting can be balanced in 5e, which after healing is the other line in the sand for warlord fans.
But there's also an additional problem for support martials in 5e, all their abilities need to make thematic sense in the broader game and that's not actually easy to do. Take action granting, haste does it, but what's a martial character doing that allows your allys another action that makes sense in the fiction. Well what is an action in the fiction? It's essentially what your character is capable of doing in a certain amount of time. How the heck is a martial supposed to have any effect on that, and especially round after round after round?
It's not just about cool mechanical abilities, it's about justifying them fictionally as well.
But I do wish you all the best of luck in getting one you all will be happy with (that's a third problem, all warlord fans want something different from the warlord). I'd like to see an official implementation and how they avoid all these potential pitfalls.