There’s also the thread Post-v5 new features and development news which tracks what’s actually new in 5.99 (the development version leading to 6.0). It’s not consistent in how small details it reports. Eeschema and symbol editor will be so radically different that it’s not possible to give very detailed explanation.
Wayne (the project leader) want’s that new features are marked with NEW in git commit messages. It would enable automatic changelog generation. But it depends on how consistently the developers actually use it. And it hasn’t been used in the past.