October 2.0 was based off of the code base as of a year ago, so everything that was added to the project in the past year was removed in 2.0. As far as breaking changes in the 1.0 & 1.1 branches go the links are mostly talking about the docs changes that indicated the removal of the recent changes; but there are some that actually cause problems for current projects that aren't upgrading, such as the removal of the wikimedia-merge-plugin which is required for plugins to load their dependencies smoothly.