But it would make a mess of the battle system we have. Optional is never a good thing when it comes to battle dynamics.
I rather they turn auto attack as a "auto skill" with a skill set of its own.
Let's make light attack and light stab an "auto skill" for instance, or change it to heavy stab/slash, etc. which the latter will increase all skill stamina usage.
Then separate TP base WS, which I refer to "instant skills" that purely rely on TP and none on stamina.
and
regular skills which are purely stamina/mp. Thus making Stamina an ATB we're all so familar with.
This would allow make the ground work for a system kind of like FF11, but more modernized, where auto attack can be changed on the fly, but will always "proc" for the intense feeling.
While you have game changers like stamina skills that are strategic.
Finally the TP skills (WS) are what you would consider, limitbreaks theories.
So in summary,
Auto attack skills (Able to switch back and forth, but proc at a pre-set rate)
Stamina skills (On cool downs and stamina requirements, stamina regen might also need to slow down)
TP skills (Only based on TP, which TP will accumulate slower) aka limit breaks.
And you can bring back a SC system this way or a BR system that only rely on TP skills.