There is no official list of features in upcoming versions since they are subject to change during the development phase.
But you can apply to join the Technology Adoption Program / TAP.
If you are accepted, you'll get access to early builds and preliminary documentation of breaking changes and new features.
http://world.episerver.com/Articles/Items/EPiServer-Early-Adoption-programs/
Hi EPiServer team
Do you have any page that shows us the next release feature list or progress/timeline?
As a EPiServer partner, when we plan to do a project using the new version, we need to make sure all we need in EPiServer 6 can be done in 7 or availability in the future versoin (e.g. Block Collection feature) or at least has an alternative solution for us to help us reduce our risk.