I came up with a little theory.
Fans thought that Game Freak's game plan was like this:
G1: R/B-Y
G2: G/S-C
G3: R/S-E (FR/LG 2 Gens After R/B)
G4: D/P-Pl (HG/SS 2 Gens After G/S)
G5: B/W-B2/W2 (?R/?S 2 Gens After R/S)
G6: X/Y-? (?D/?P 2 Gens After D/P)
etc....
But maybe, what if...