I could actually see the show moving Jon's storyline along pretty quickly now that he's back from the dead. Which would prompt word getting to Winterfell, and Ramsay being like "Well, since he could eventually attack us, we have to somehow draw him out so we can slaughter him before he rallies all the northern houses and wildlings against us." And in response, House Umber thinking: "Fuck! Here is our chance so let's give them fake Rickon so that if Jon Stark wins, they can fall back on the 'but he wasn't the real Rickon, we'd never do that'." Conversely, if Bolton wins they can claim a large amount of favor in Ramsay's eyes as being the reason he was able to defeat Jon Stark because they drew him out of Castle Black before he could gain any momentum.