I think there are also logistical issues regarding, but yeah, as far as character stuff goes, this describes my other concerns perfectly.secret and false identities and the broader pro-Lannister politics of the Boltons
Yeah. I think most of the logistical issues go away if she's there as Alayne, and the marriage is to win Bolton military and economic support from the Vale. If she's there as Sansa, though, then it becomes kind of a mess. Why are Bolton and Baelish both openly defying their patron, Cersei? She hasn't had her downfall yet, and still commands the entire Lannister/Tyrell force. And if she's Sansa, why would Bolton give her free roam of the castle? He would have to know that while she's a valuable hostage, she's also a threat, and that she should never be allowed to be alone with anyone. If she were Alayne, then it would make sense that she could move freely and then reveal herself in secret to those she trusts, but the real Sansa should basically be under lockdown.