So I was thinking about the Super-Specials or Smash-Specials concept that's thrown around here sometimes and while it's not something I've ever really considered on my own before I'm starting to understand the application of the idea could very well spice up the game in the same way my other moveset expansion ideas would. My defacto main already has this concept and I'm surprised I hadn't considered it moving to the rest of the cast before seeing the idea discussed here.
I think there are 2 applications to the idea currently in-game and unless somebody here can get creative I think that's the extent of how this potential mechanic could be universally applied to the entire cast. We have the Cloud model and the Joker model. Cloud's specials dramatically improve while Joker's kind of gets everything by being in an empowered state. There's one more layer to consider with how they acquire their meter. Cloud can actively generate his meter while Joker must appropriately time landing what is essentially a counter with it quite literally becoming one in the empowered state.
I think both of these models are an acceptable approach and would be dispersed throughout the cast on a case-by-case basis. You could even mix the 2 layers with having a character actively generate their Super-Special meter to get into an empowered Arsene-esque state and another where timing your counters powers up your individual specials dramatically for one hit.
The only thing about this application is that these Super-Special meter mechanics (the charge/counter) would require their own unique button I feel like because you can't just get rid of everyones' Down-Specials to fit them there. I think it'd be perfectly fine though since there's already room for this on either the X or Y buttons.
These could also be uniquely themed if the character warrants it like Cloud's and Joker's are already in the game. Otherwise it'd just be a generic meter I feel like though maybe the graphic design team could have some fun and all some charm by giving each character's meter appropriate aesthetical flair.
Oh well it's just a super interesting proposal I feel like. Coupled with some of my other moveset expansion ideas like Aerial-Smash-Attacks, Super-Smash-Attacks (Terry's Go command inputs attacks given to the cast see my moveset expansion ideas for a deeper dive if interested) universal counters (could take the spot of either X or Y button as well) and a competitive Final Smash overhaul (again deeper dive in my moveset expansion ideas in my signature) would REALLY spice up this game tremendously.
I don't think a universal super meter needs a universal way to charge it tbh. I think the standard fighting game method of it charging by landing hits and taking hits will be just fine.
Certain characters can certainly have their own ways to charge it. In addition to Cloud and Joker's existing ways, we can also make it so that Ness and Lucas's PSI Magnet can steal super charge if it hits, essentially how it works in the MOTHER series.
About Final Smash being competitive: I think that's a lost cause that's best left as an uber-powerful unique item that isn't meant to be balanced.