RC pools is one big thing I know of. I believe there are some improvements to how vote changing works.

I'm pretty sure there are other things but we will have to wait for the release notes to know what they are (or dig through github logs).

Overall the development process is pretty linear. Any work that has been done since the last hard fork and not specifically put on a parallel track (which is rare, since it significantly increases the development effort to maintain parallel code bases) will end up in the next one.