Yeah, I really hope it's lots of cool recharge abilities. Something pretty dangerous that can be used once, and then recharges on a crit. By assuming it's used in the first round the CR can be modeled appropriately, and then after that the players will usually* have a one round forewarning that it could be used again, and can prepare accordingly.
Personally, I think "Holy $%#& we have to neutralize this monster before its next turn!" is way more interesting as a game mechanic than "Let's hope it doesn't roll a 20."
*Unless the monster has multi-attack. But it could be written into the rules that recharge doesn't take effect until the following turn. In fact, it would have to be written that way if they didn't want a lucky monster to be able to use it multiple times in a turn.
EDIT: Oh, and weaker monsters could be designed to start combat without the recharge ability, so no initial spike. I mean, it could be as simple as "On a hit, the creature rolls rolls double damage dice. (Recharge)." It's a crit with foreshadowing.
EDIT 2: Thinking more about this, I really like the idea of this kind of foreshadowing. It changes the calculus on decision-making, and elevates abilities like Frostbite and Dodge. And/or, instead of "hit the goblin with the fewest hit points because they are all equal threats" it's "well, should I finish off this one, or see if in one turn I can kill the one who is about to crit?" It adds variability to monsters in a single stat block.