Do not know if this has been brought up, but it would be nice to have a Task Tracker for each Mercenary. I never remember on what level of their task are my mercenaries when Mysterious Stranger pops and it would make it much easier to decide which Mercenarie to select depending on what I want to advance on their task level.
Also, in PVE it would be nice a description of the bosses, like their composition, special attacks, resistance, etc. When I do Heroics and get to the boss just to find out that my team composition is bad for that boss and loss and have to do it all over again.
I do not always play Mercenaries to remember well what comps fit better for the boss I am trying to finish especially in Heroic, where they keep getting harder and harder.
On excess coins, I know this has been brought up lots of times, maybe make them able to use them to buy portraits after you have maxed that mercenary.
Other than this, I have been having fun with this mode and enjoy it, love the PVP part too.