1 key action = 1 action

Is fine, currently because Blizzard has specifically put this function into the Keyboard API, which addons can use. To my knowledge, at the moment, Snowfall and Macaroon are the only addons that use this feature.

Press Down = an action.
Release = an action.

It is easy enough to do a two step mapped key.
With an action on release of each key, which is the default.