To be honest, I don't know much about Russian history during this time, but I was looking for ideas & I found the Moscow Uprising of 1648 (A.K.A. the Salt Riot). What if Tsar Alexis I is somehow killed during it, leaving his son Dmitry(who was born that August) in charge? If Dmitry dies the following year as OTL, the only male Romanov left alive is Alexis’s 1st cousin-once-removed Nikita, who is not a descendent of Tsar Michael I & is very big on European culture. Could this lead to a second Time of Troubles, ending in a new dynasty ruling Russia? Could Sweden, Poland, or the Ottoman Empire take advantage of the situation?