With this you could still attack 4 times with flurry of blows AND do burning hands in the same round though.
True. Though a sorcerer/fighter could do the same thing with quicken burning hands + action surge + extra attack. Granted that's a multiclass build vs a single class monk, but it's a single class monk that just isn't very good otherwise.
When you get into multiclassing, You could cast a bonus action spell or a quickened spell and still get 4 attacks in as well.
Yes, though again, you don't need monk to do this. Sorcerer + Action Surge gets you this already
Action surge and this would allow you to attack 4 times, cast a bonus action spell, and cast a standard spell.
This is more powerful, but requires 2 ki points, 2 SP and action surge, and a level 10 character with at the bare minimum, with a caster level of only 3. At level 10 as a Monk 5 / Sorcerer 3 / Fighter 2, you're spending 2/3 of your daily SP, your one action surge / SR, your one bonus bonus action / SR, and both your highest level spell slots to do something like 10d6+2d10+16 damage on hits (assuming a scorching ray, a firebolt, and four punches). Figure a 60% chance to hit, that's about 37 damage total, possibly with some conditions inflicted if you spend more ki. That's roughly on par with what Animate Objects can do every round with a bonus action at that level. The fact that to get this you're restricting yourself to 2nd level spells at level 10 is a big factor.
Or you could cast 2 standard action spells a quickened spell and dodge/disengage/dash.
I doubt anyone is going to complain about somebody getting a free dodge/disengage/dash once per short rest.
A super MAD Fighter/Monk/Sorc combo with twin and quicken could effectively generate 5 spells in a single round AND still get a bonus action to do something else with.
Yes, but four of them have to be cantrips, and the other one is 2nd level max, unless we're going to even higher levels. And the bonus action is the only new part here. So a lot turns on how powerful that thing is. What bonus action options would you have with that build? Other than dodge/disengage/dash for more ki?
My post even said that something like this wouldn't be super OP, just that it could have some wonky consequences on encounter balance because of breaking action economy, especially when combined with other things that break action economy.
There might be some combos I'm not thinking of, but that's what this thread is for, right? Can you come up with any that are beyond what a character can normally do at a corresponding level? And if they're not beyond, are they sufficiently close that you'd argue that getting to do it on top of other things that build can do makes it OP at all even?