Red Alert is my favorite universe in the series and I would love to see them make Red Alert 4. I for one would like to see a more gritty and realistic looking RA game. Maybe have the same graphic style as TW/Generals 2 where the game looks more serious.
Of course all 3 of the factions from RA3 should return with some of our favorite units and make a few new ones.
As for the story f the game I would like to see some sort of problem occurring in the timeline because of all the time travel that has been happening. Maybe there could be a fourth faction that is based off of energy/plasma where they exist in between dimensions and are sent to earth when a time rip opens.
And if they decide to make this game I would assume it could be sometime between 2014 - 2016. So that way it would follow the trend of having a new game made at least 5 years after the last one.