I wouldn't mind seeing more crew rotation in a Trek series. As I just pointed out in another thread, in real life a typical military tour of duty is usually around 1-3 years, maybe even less. The same crew serving together on the same ship for 7 years is very unrealistic. Especially when they're facing traumatic, life-and-death crises a couple of dozen times a year. After a few years of that, they'd be basket cases.