Marketing-wise, it doesn't make sense to market a sequel without any links theme-wise. X & Y share nothing with Sun and Moon to link them as sequels, besides the color, which is a stretch, as the designs for the logos do not match style-wise & the sun & moon emblems aren't red & blue like the X & Y emblems.
It would be the first time that Nintendo made 2 sets of games in the same generation that weren't explicitly stated as being sequels.
>Gold and Silver were in a separate generation, but still sequels to Red & Blue, a likely possibility for Sun & Moon, considering the parallels between gen 1 & gen 6
>Black & White 2 were explicit sequels, due to the obvious shared name and sequel notation.
Also, if they are going to be gen 6 sequels, what does the sun have to do with Xerneas and the moon have to do with Yveltal? Also, explain the change in colors, from the blue X to an orange sun & the red Y to a blue moon, or how the reverse would make sense.