Generally a "surprise" round tends to be a decent compromise, which is a round in which the "ambushing" characters get half of a turn to act first and then initiative order comes into play.
So, if a character got 4AP every turn normally, then they'd have 2AP in the "surprise round," etc. After all the "ambushing" characters have taken their "surprise round" then the battle begins with initiative order. (Which means if the ambushing characters have higher initiative, they would act again before your party does).
This could be cool - but with amount of disappointment from some players at the current ambush difficulty I'd say unnecessary. Still, if they wanted to add it in the higher difficulty modes it could be fun. Do I get the same benefit for opening from stealth?