My bet: Observer mode like in Smite, everyone who wants(and can find a game via playing friend) can join with 3 minute delay.
I believe League and DOTA2 have something like a 2 minute delay so it is okay
Problem with that is MG's, Mortars, AT Guns, and especially mines and bunkers don't just sit around for 1-2 minutes. If an observer sees a mine being planted, he can tell the other player where this mine is.
I don't think real time is fair. First, there is bound to be a delay because of lag. Secondly, even though you are only spectating one side, you can have people "spot" for you which is still cheating.
How is it any worse than people giving advise to streamers or having 2 people at a computer (one playing, one watching/"spotting"). Sure, it's an advantage, but so is having naturally faster reaction times.