Guess that some (Bonus) action can be worded similar to fighters Action surge and some just molded into Action.
This means the "Used to be Bonus Action spells abilities" always have to be used before another action. That might be ok for effects that are intended to boost your next attack, that is quite restrictive and limits tactics for any other Bonus Action-style actions. For example:
Misty step.
Action. Teleport 30ft,
you can immediate take another action except casting a spell with a spell slot.
So you can't attack someone and then Misty Step? Not interested.
Hunters mark/hex/divine favor/smite
Action.
you can immediate take Attack action or cast a cantrip
I suppose this can work, but it still does not allow the Ranger to cast Conjure Barrage, then Hunter's Mark whoever is left standing. (That is a bad example due to two spells, but it essentially disallows other Actions before casting Hunter's Mark.
Wild shape.
Action. Turn into an animal.
Immediately take another action from animals stat block.
So you can't cast Call Lighting on Round 1, then turn into an eagle on Round 2 and use the Magic action to use your Call Lightning while flying?
Rage.
Action. You gain Rage.
immediately make an Attack action
This one is would work ok.
Dash.
Action. Move your speed. Or move twice your speed in a straight line over non-difficult terrain.
Dash is already an Action (unless you have another ability making it a Bonus action.)
Flurry of blows.
Add 2 unarmed attacks to your Attack action.
Sure, this would work. The wording would be something like "Make 3 attacks, at least 2 of which must be unarmed strikes."
GWM,
when you score a crit during your Attack action, add one more attack with that weapon to your Attack action.
Sure.
(Mass)Healing word.
Action.
after casting healing word you can cast a cantrip or take Attack action
Again, like Misty Step, this suffers from not being able to choose when you cast the spell vs the other action.
Command a pet/companion/mount/familiar/whatever
Give command(s) to your companion(s).
you can take any action after this except another Command Action.
The wording of abilities like this would be so weird, cascading into other multiple actions. Can you Command your pet, then use that action to cast Hunter's Mark, then use that given action to make the attack that Hunter's Mark gives you?
Basically we would still need to designate special terms for these "bonus action-style Actions" to limit how they are used/stacked.
I disagree with Mike Mearls on this one. Bonus actions allow for a broader array of tactics and flexibility of options on one's turn. The checks and balances that need to be created to manage how to use "multi-action Actions" may need to be more detailed than Bonus Actions as-is, with the added side effect of removing flexibility.