Anyway, I think your proposed revised action list is a little unclear. Unfortunately, that's not really your fault because the rules already have a gaping hole (since even 3.X edition) in that there's not a clear definition of wield vs. hold. If we still ignore that such that no one would ever simply want to hold a shield, I would change it like this (assuming like you said all shields have a guige):
- Bar grip (only):
- drop as a free action
- stow as a minor action
- Enarmes (only):
- drop as a minor action
- stow as a standard action
The reason why I mentioned wield vs. hold is because with enarmes you're missing that option. It doesn't make sense that you can stow with a bar grip as a minor and you can't stow with enarmes as two minors (since you can loosen/drop it as a minor). I would consider allowing stowing with enarmes as two minors, but then we need to define the state of the shield after the first minor.
Unfortunately, in game terms, using the above alone is insufficient. Bar grip is clearly superior to enarmes in every way, so no PC would ever choose enarmes. What benefit would they provide? Specifically, is it even worth considering game benefits in a system that no longer allows disarming? I can't think of a benefit that wouldn't totally throw the system out of whack (perhaps something with skill checks, or a +1 bonus on bull rushing), so I'd be tempted to just go with one of the sets rules regarding
all shields. It seems like Wizards chose enarmes. Thus, dropping a shield is clearly a minor action. QED.