I have to disagree with you. I'll be really surprised if Sam/Cas get more than one or two scene together without Dean in the WHOLE season (and I'm sure they will talk about Dean and if possible have Cas stress how much closer he is to Dean not to upset certain fans who are already complaining about this spoiler). And the writers would never let Cas interact with Sam as much as with Dean (best case "Pollyanna" scenario is 5:1 on Dean/Cas to Sam/Cas scenes), and after 8.10 he'll probably interact with Naomi more than with Sam.

And It doesn't matter if Sam wants to be there or not. He is still part of the story.
Going by Jared's shooting schedule this "Sam story line" has to be playing out off screen then since even Benny is getting more character focus and actual screen time than Sam (and more big scenes with Dean). And now in the second half Cas seems to be taking over for Benny.