Sounds very complicated. Far more so than ‘you get one bonus action per round.’
Complicated how again?
Complicated when making a decision in play? Complicated to write out?
I am aiming for simplicity in play. And by that I mean makes making decisions on a round by round basis simple, and not connecting all of the whirling widgets in the build you make to output an optimal turn.
Interacting with the world, sure that can be interesting. But I'm less interested in internal mechanical build complexity, so I say we strip it out.
Fighters don’t need any help with power. Rogues have been helped with steady aim. You don’t change the action system just to fix monks. Change monk abilities instead.
Are they so powerful that we must not give them anything? The goal isn't "more power" it is game play.
My claim is that the impact on power increase is not large enough to be problem.
Unlimited bonus actions give fighters the ability to two weapon fight and second wind on the same turn. That is naughty word all of a power swing. Is it more power? Sure, but not to a degree that
matters.
This isn't about powering up characters for the most part. Saying "they don't need a power up" is irrelevant, unless you are saying "it would be bad for the game if they gained this power".
In that case, how much power do you really think this is?
Lets look at pure class characters for now.
1) EK can cantrip, bonus action spell, second wind, and make an attack at level 7.
All of the power up uses strategic resources. Almost no impact on long term power, just a slightly higher short term power spike.
2) Monk can make a Martial arts attack. Then spend a Ki to either do 1 more attack (Flurry instead of MA), dodge or dash. Basically, when dodging/dashing they get an extra attack. (All of their Ki features are under the Ki feature, so they have to pick one; but MA is not).
3) TWF/PAM/XBE fighters/barbarians/rogues/rangers can use their class features along with their attacks. So rage+twf, rage+PAM, hand xbow attack+disengage/dash, PAM+second wind.
This is a slight power increase, but mostly it is a build variety increase. If your build depends on bonus actions you avoid fighting styles that use that bonus action attack. And if you want that bonus action attack, you avoid builds that use bonus actions.
Similarly for a GWM who crits or drops a foe; unless they have PAM, they can just do the attack, even if they had used a class feature.
4) A Bladesinger can ramp a bit faster; they can bladesing and shadowblade on the same turn.
5) A TWF paladin can cast smite spells while swinging their offhand weapon.
6) Rangers no longer have bonus action constipation in general.
I'm really looking for something that breaks all that much.
Analysis paralysis between choosing between three options? Really. If you need the move you take the move. If you’re attacking someone take the +1 to hit. If neither apply then take the AC. Not sure how that is difficult.... and definitely not more difficult than the multiple categories of bonus actions that you think are needed.
Whenever a player makes a decision, the decision should matter. There is a table time cost for making decisions, not only in the time to make the decision, but remembering you have to make it, dealing with forgetting it, etc. So decisions should be interesting and have good and fiction mechanical impact. Any decision that has no good and fiction mechanical impact should be removed.
This isn't TTRPG balance stuff, this is basic game design. Don't waste people's times with fiddly crap by default. Don't waste my time with fiddly crap.