I love this idea and I'd be all over it. One thing I don't like about how they've dealt with hero units in the past though - they never really feel very heroic. Like if I have that unit geared to a certain threshold I feel like any mission I use them in should be easy - or at least significantly less hard. If we're going to call them a hero, let's put some real heroics in place.
I'd be 100% on board with calling out a few underutilized but thematic characters to actually have an impact on the difficulty of missions. Great idea Seedy.