jaelis
Oh this is where the title goes?
Perhaps Second wind could be changed to "As a bonus action, you can spend one of your Hit Dice to regain hit points, in the same way that you can do during a short rest."
Check out the 4E rules sometime

Perhaps Second wind could be changed to "As a bonus action, you can spend one of your Hit Dice to regain hit points, in the same way that you can do during a short rest."
If it works for you, that's cool. You're combining two pools of energy together, which isn't necessarily a bad thing or impossible to do.
Using your hit point example... you currently have a pool of "energy" (hit points) that is worth a certain number of points. And you spend those points doing stuff (like resist getting knocked out.) And you can only do stuff until the pool is empty, at which point you need to rest in order to refill your energy pool.
Action Surge is the same thing, except that it's a pool of 1 point. You have a pool of "energy" that's 1 point deep and once you spend up to it you have to rest. Just like hit points might be a pool 25 points deep and once you spend up to it you have to rest. Or ki might be a pool 4 points deep and once you spend up to it you have to rest. Or Lay On Hands, or Sorcery points, etc. The mechanics are all pretty much the same. But the game creates this differing pools just because they tend to be easier for people to grasp and understand, and easier for them to balance.
But if you want to try and start combining all these pools together, that's great. Best of luck with that, and it'd probably be an interesting design challenge to get it balanced. The game already has another "alternative pooling" system in place with the Spell Point variant rule, where they switch over individually-leveled pools of spell slots into one massive "spell pool" of points with which you can spend them to cast spells. And indeed, I've seen people attempt something like you are talking about by trying to combine the "Spell Point" pool and the "Sorcery Point" pool together to form one cohesive system for the sorcerer class where both spells and metamagic are paid for out of this combined pool. Which is why I don't dismiss your idea out of hand.
The real question just ends up being whether Fighters actually need to be able to take additional Action Surges for the game to work better? What is gained from them getting that, other than this idea that being able to only do a fighter activity "one" time before resting doesn't "make sense"? There's a lot of stuff in D&D that doesn't "make sense" and can "break immersion"... so that's part of your dilemma. Why does this fighter activity warrant trying to re-write the rules for yourself, but so many other nonsensical things in the game don't?
It's the age-old question any of us who fiddle with the rules end up asking. I do it all the time. I find something in the game I think could be done differently... I spend an inordinate amount of time futzing with things to try and get it to work... and then once I'm done I look at what I've put together and then honestly think to myself "Will this thing I've put together make any ACTUAL appreciable difference at the table if my players use it?" Or is it just one more oddity of a mechanical system that my players will use if I ask them to... but which won't actually result in my game feeling different?
Usually the answer is 'No'. And why? Because so much of the game is roleplaying, and *not* game mechanics. Which means any individual game mechanic gets used so infrequently that any problem with it comes and goes and I barely notice it during play. It's only BETWEEN games or BETWEEN campaigns that my mind wanders around thinking "You know, this might be better if it worked like..." But once I'm in the game itself... any problems I might've perceived out of it, almost never get perceived while within.
Good luck to you!
I agree that it's kind of weird for a non-magical character to have a hard limit on ability usage. When you use HP (or hit dice) as an alternative limit, that doesn't make it less weird, because HP is an inherently weird mechanic in this edition. Whether it's more-weird or less-weird is a matter of opinion, but I personally don't see it as a favorable trade-off to ditch the hard-limit abstraction in favor of the HP abstraction.Opinions?
That is an issue. Even just two levels can be severely detrimental. If you wanted to use that as your metric, I would recommend making a Constitution save with a scaling DC for each use, and only giving an Exhaustion level on a failure.Problem with exhaustion levels is that they are such a bummer to have.