A slight variation I'm doing for my custom ruleset is that when you get skill specializations, you choose two subskills and gain a bonus on those subskills. I could see it also being extended that you could do stunts related to those named subskills, especially them being little tricks you can do, without having to making a skill roll to pull them off.
So, for example, you might have Athletics. Subskills could be Jump, Climb, Swim, etc. A stunt might be to do a kip-up with Jump so you only use 5 ft. when standing back up. But at the same time, not restrict it to only a narrow set of subskills - just give some examples. Same with the stunts - negotiate with the player what sort of stunts you can pull off (and if you need to, write down the mechanics if it's needed for later).
One thing I learned from the design of the Chronicles of Ramlar & 3E long ago (and Daggerheart recently) is there is a diminishing value of return if you too narrowly define skills, backgrounds or the like. Keep them broad, don't be stingy with the mechanics ("You must have the Kip-up subskill to do that" - nah, specialization with Jumping is more than enough) and be willing to negotiate with the players based on their character concept and what's happening in the story for it makes sense. Because sometimes, DMs try to get too far into the weeds with "mother-may-I" systems from what was initially meant to add a little pep to their game.