Something that stood out in s10 was that absolutely no one in-show was interested in addressing how the trauma of the events of s9-10 affected Sam - I'm including Sam in that count. I mean, Sam was already injured, Dean had just tried to kill him with a hammer, and Cas didn't want him to take time to sleep before pressing on to find a cure (10.03). That, along with everything else from s10, is going to catch up to him. (The mock execution, for example.)

I'd love to see someone in-show taking the time to consider how Sam's being affected by events and try to help him. Anyone still technically alive at the end of s10 is fair game, even if it's technically a villain like Rowena.