An update to let you know what breaking changes we are doing in CMS later this year. For many sites the changes will go unnoticed, just another major version number, the latest version of the Alloy templates for example requires no code changes - just recompile and you are done.
Remove hard dependency on Log4Net. This will make it possible to run on the latest version of Log4Net or use another provider. Link to SDK.
As previously announced we will remove our implementation of WWF (Windows Workflow Foundation), where WWF 3 that we are using is now obsoleted and (officially) not supported on Azure. We are instead investing in "Projects 2.0" and you can follow the release feed to see this beta feature light up and support rich collaboration on not just pages but block, media and catalog content.
Remove remains of the VPP system that was obsoleted in CMS 7.5. Link to SDK.
Remove assemblies EPiServer.BaseLibrary.dll and EPiServer.Implementation.dll. These assemblies was the framework of CMS 5 and contained internal features such as the ObjectStore. There are a few classes in there still used that are being moved to EPiServer.dll.
Disable Dynamic Properties by default. As officially annonced in 7.5 this feature does not support the new user interface. We know there will be a lot of sites upgrading that are using dynamic properties so it will be left intact and there will be a setting to enable/disable this feature.
Release later this year with more details. See this post by Magnus for updates on planned breaking changes in Commerce.