I always thought they pretty much covered Clana in season 5, but really I think their big mistake was always not just getting on with Clana when they were supposed to be high school sweethearts, instead of forcing the on/off thing for drama. It felt kind of pointless to spend season 4 on Jason/Lana when they could have spend that time on Clana, and have more relevance to Clark's journey but oh well *sighs*

And yep, it will never be the same without Lex, but I am also totally excited for this season :D