I think that the ruy lopez will have a revolution somewhere which would help white or black. The Marshall Gambit might be analysed out to a definite conclusion would be my guess.
I think that the less popular openings will make their mark again as the ruy lopez would be analysed out. Maybe the Italian will come back with a new revolution in the Two Knights Defense, showing that black does not have enough play for the pawn after 1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5. White must find somewhere to improve with 3...Bc5 to have the popularity rise again. Maybe with the Powtow Attack? An improvement in the Mueller or Rossolimo Variations? Possibly the Evans or Italian Gambits.
The Scotch would be a good candidate as it has not been greatly popular and it has not been analysed to a great depth. If a great player will pick it up and win convincingly with it, then we will see a resurgence.
The only thing is if these become to popular then black might turn back to the Petrov Defense and white would have to adjust.
How many times have you seen or played a middlegame in which the differences between relative piece values seemed to be erased throughout? I believe that openings like those will be the ones absolutely dominating the chess scene in two or three decades, more absolutely than ever. They already offer oceans of dynamic complications, so as the novelties spring almost every day, it could be possible that any endgame-ish openings would fall out of favor for lack of resources, but that's just my thinking. As of the present, such openings would include the ones that are currently theoretically overweight, mainly the Sicilian Najdorf, Dragon and Dragadorf variations, the Semi-Slav Botvinnik variation, and...? Any ideas? My guess is that the ever-resourceful Ruy Lopez will survive, so will the KID, specifically the Bayonet Attack and the Saemisch Variation, I guess (at least I know some marvellous middlegame examples in both cases). The Nimzo-Indian should also survive, maybe the Scotch will hit the spotlight once again, and the common old gambits would be extinct. Or would it all be the other way round? You tell me, when you're between a Chuck and a Vlad place!