[theoriginaldog]

Ready an action is only usable in combat, so RAW outside of combat readying actions to jump on people you lured with an illusion into a room is not possible. This is an ambush and would be dealt with stealth / surprise rules and THAT is in the game, so it is possible if you play it by the rules.

The ready action is designed to get used for delaying actions to bypass initiative order.

[wlesieutre]

Is it considered weird to drop into combat grid and initiative order to handle action strategy like trying to dodge around a guard patrol, even if nobody's been stabbed yet and nobody might get stabbed at all?

Speaking of delay, I know that's not part of 5e (it was in 3.5), but if we can't have ready action could we at least have the delay option? A lot simpler to implement and it'd at least help with the situations where you would have been better off at worse initiative.