Acceleo is on Ohloh, thus you can access information about the commits, projects news, code metrics... directly on its page.
New & Noteworthy
Check the New And Noteworthy page for information on notable evolutions for each version.
Check the Release Review page for information on the release review for each version.
Check the API Policy page for information about Acceleo code aspects : what is considered API, how is API maintained...
Check the Retention Policy page for information about the code and build retention policy applied on Acceleo.
In the Acceleo wishlist page, you can find a list of features that have be requested for Acceleo and that are for now not in the roadmap. As such, those features may appear on day in Acceleo but they are not the priority. In someone want to contribute to Acceleo, realizing one of those features is a great start.