This release adds an update that clears caches, preventing an error some users experienced after updating to 8.x-3.0. Specifically, it adds an update to rebuild the service container, preventing an error in the features.manager service. If you have already updated to 8.x-3.0 without problem, there is no need to update to 8.x-3.1.
This alpha release includes major refactoring. Sites upgrading from a previous alpha release will need to uninstall the previous version of Features and Features UI and install fresh using the new version.