My best guess to the release schedule at this point, going by Japanese release dates, is:
Summer/Fall 2013: RS remakes (DS)
Fall 2014: Gen VI paired versions (3DS)
Fall 2015: Gen VI third version or sequels (3DS)
Spring 2016: RG remakes (3DS) - 20th anniversary
Fall 2016: DP remakes (3DS) - 10th anniversary
Fall 2018: Gen VII paired versions ("4DS")
I doubt Game Freak has anything planned out longer than that.
I doubt they even have half of that planned out.
They might have vague plans in the background sure, but they probably don't actually take them into serious consideration until the time when they will get around actually developing them.