Happy new year!
These year I'll write about monsters, weapons, yadda yadda, let us skip this stuff for now.
So, here is a brief idea after a long hiatus. Hopefully, I'll get back to blogging soon enough.
TL;DR: I'm considering allowing PCs to trade half their move (or their main action) for an additional bonus action.
I like the whole "action economy" of 5e. I think they've got it (mostly) nailed with actions, bonus actions and reactions, with a few exceptions - two weapon fighting, Beastmaster Rangers, etc.
However, Mike Mearls himself has suggested that it might be a good idea to get rid of bonus actions.
I often wonder about the same topic.
The most obvious solution would be trading some MOVEMENT for special actions - dodge, disengage, hide, etc. Use "half your movement" as a baseline. Not too different from getting up if you're prone, for example, or how disengage worked in B/X.
Other simple actions could be "part of your attack". Drawing a knife or arrow, for example. Drawing a zweihander might cost you some movement, so an unprepared warrior with a heavy weapon would be less mobile. Nice!
Other things - like rage, for example - might be better portrayed as reactions. I like the barbarians' rage triggering in response to some event, at least in the first few levels.
What about bonus action spells? Well, I'm not the greatest fan TBH. Most of them seem to be created to allow you to create a special weapon and attack with it. So, just add hat to the spell's description.
In short... bonus action serves as an abbreviation, a shortcut to the idea that you can do this "thing" and still get your main action, but you cannot do two of these "things" in the same round. Which is not always a good thing - rangers, for example, have too much stuff competing for their actions.
In short, the whole "bonus action" concept isn't necessary... but a good enough shortcut. Because of that, I am not sure if getting rid of them would make the game any simpler.
If I were to make a "realistic" system from that, I'd probably give each character a few TOKENS representing their movement. Say, one blue token for each 5 feet of movement (these can be used for various kinds of movement). Then one red token for each attack or spell (a fighter with four attacks gains four tokens). Whoever surprises the other side, rolls high enough for initiative, has some rogue-like reflexes, etc., gains a few green tokens that cannot be used, only held until the end of the round.
The creature with the most tokens acts first, spending some of their tokens - maybe from one to three, at most.
So, the fighter with four attacks can probably pull a knife and stab a CR 1 monster three times before it reacts... But if he has a battleaxe, he might have to spend a couple of blue tokens to draw it before attacking, which might be enough to let you attack back, unless you're surprised, etc.
This would lead to more "organic" battles, as I intended here.
These lead to endless permutations, of course. Tokens for reactions - why not? Additional tokens for critical hits of misses, maybe depending on weapon speed, etc.
Probably too much work for little effect. But something I would definitely use for a more "tactical" version of D&D in line with 4e, etc.
For now, I might just allow PCs to trade half their move (or their main action) for an additional bonus action. Maybe fighters get one additional bonus action for extra attack, provided they use it for TWF, etc.
Next: maybe a(nother) simple yet detailed "fix" for two-weapon fighting or weapon speed, based on this post.