Since current core sets all have a returning mechanic of some kind - usually a keyword, although Magic 2014 used "Sliver tribal" for its old-is-new-again theme - each year there is speculation about what the one for the upcoming core set will be. The mechanics in question have to be simple, relatively neutral flavorfully, and lead to good gameplay and interesting decisions for even beginners, and Mark Rosewater recently advocated one oft-repeated mechanic for the slot.
When openfire1 asked Rosewater on his Tumblr blog, "What would be the chance of Cycling being the main mechanic of a core set? And if it was, what colors do you think it would be placed in?" he said:
Cycling could be in a core set. I have no idea what colors would get it. It depends how we used it/what type of spells we put it on.
Almost every color but white is a "natural" fit for cycling. Blue obviously has hand filtering and card draw and "pursuit of enlightenment" flavor, black is willing to discard as a cost and fill up its graveyard, as well as to throw away lesser resources callously, red is impulsive and nowadays gets looting effects in its slice of the color pie, and green is tertiary in card draw and has an idea of "mulching." However, since core set keywords are typically relegated to two or three colors, blue and red seem most likely, since cycling is able to be used as an instant or sorcery mechanic as well as a creature one.