Wouldn't this make good II/IR Encounters too good?
You use an At-Will Standard and an II/IR encounter every round (if you can) until you run out of Encounters and then you sacrifice a chance to use an At-Will to gain the ability to do an Encounter (and this assumes you haven't killed everything by having built to do 2 attack powers every turn so far - especially for Strikers who get damage bonuses "per turn" now). Seems a no-brainer to me.
I suppose the II/IR powers may be underpowered for Encounters, but they are still better than an At-Will I find (especially some of the Ranger ones - those are basically just a typical EncPower off-turn).
EDIT:
Never let this rule loose around a high level Wizard. Steal Time (Lvl 27 Enc) becomes perma-stun of a mob as it gives you a StdAction when you hit with it, so you can use that to regain Steal Time and use it again once the stun wears off. Also TimeStop gives non-attack StdActions (2 of them) which would be a bit sick, especially for a Lvl 30 Lorekeeper - who can make TimeStop an Enc, so every turn you use TimeStop to regain an Encounter power and itself for the expenditure of a Minor.
Similar issues hit at Paragon with the Life Singer Bard's Lvl 12 Daily Utility. The Bard spends one StdAction to potentially give the entire party an extra non-attack StdAction. So one Lvl 12 Utility becomes "Every target regains an Encounter Power" which is way too nice.