Yes to these.
I don't think we've seen the last of Rachel, at least I hope we haven't. She started out as a total bitch but I really like the way she's turned a corner and realised how important her daughter is to her. Personally, I think that a family threesome (MC, D, and Rachel) would actually be a really sweet and emotional moment for the three of them to have. It would really allow Rachel to show just how much she's changed and how much she truly loves her daughter as well as allowing her and the MC to both reconcile and find closure at the same time.
As for Cassandra, I'd very much to see her and D together without the MC being there. I think it would give Cassandra such a shock to find out just how confident and experienced D is with other women, and it would be cool if D turns the table on her by taking the lead.
We'll get Jennifer in the next update, or rather when the completed version of this update is released with the final update, because there will be an Elena/Jennifer scene if you're on both those paths, and according to the walkthrough these path will eventually merge into a D/Elena/Jennifer path so I think her future with the MC looks fairly set. Now we just need Mr Dots to allows us to have both Georgina and Jennifer and then we're all set.