I'm not sure how that would interact with the rest of the game. Probably badly. I know all the PCs with
shield would hate it!
Yes, I am aware it is not a simple house rule. I was pondering it more for a ground up re-build. I like the simplicity of action, bonus action, & reaction. However, in reality 5e allows multiple "saving throw actions" or "ability check actions." Right now those are free actions (check sometimes have a cost); however, in general I assume the character is actually doing something to achieve the check or save, so I feel it should have a cost. iI was interested in the idea of set number of actions that can be spent on different things. Something like, you get:
Action: a standard action used on your turn
Minor Action: an action that takes less time or effort than a standard action
Bonus Action: a minor action you spend on your turn
Reaction: a minor action you spend off-turn
Saving Throw: an action or minor action used to mitigate an attack or effect. Usually a reaction.
Check: an action or minor action used to adjudicate the outcomes of uncertain events.
A character gets one action and two minor actions per round.
Thus you could use a reaction, and a saving throw, but not two saving throws and/ or a bonus action in the same round. It might be possible to say an action = 2 minor actions and provide even more flexibility.