Since Second Wind does more healing than hit dice after you've gained a handful of levels, you are not losing anything by burning the hit dice and gaining free hit points. Adding Action Surge on top of that would be way over the top. You can't guarantee a particular class will be front or back line, archer fighters exist and would love that trade in.It depends on what they power & how. I bet if I had said "burning a hitdie to recover second wibd & action surge but I'm not sure if it should recover one or both" your post would have looked very different... Burn a hit die to recover our rages?... maybe... Burn a hit die to make this bow shot a line or burst? same deal... Burn a hit die to cast one of these spells/spell like abilities?.. how is that any different from the prior examples other than being unfinished? The key is that everyone needs to want to use them, right now backline classes hardly ever use their hit dice for anything and they have nothing to use them on
@Kinematics I think the point is more using hit dice to recover or power balanced amounts of short rest abilities & designing those abilities accordingly so everyone has a decent selection of go to powers that way. Of course it would require not having a couple munchkin classes built entirely to abuse the 5mwd.
I think the mechanism would unfairly punish characters who are more likely to take damage. They need to balance reserving enough hit dice to stay on their feet vs refreshing abilities. Characters less likely to take damage can be more gung ho and spend more on refreshing. I know which one I'd find more fun playing.