Beta1 and extensions

In Vancouver (and before that in Brussels), we were talking about beta
releases and what we would expect from extension. Someone (I think it
was Peter E) suggested that we add something about that to the release
notes. Here is a draft:

After the beta1 release (scheduled for June), we suggest that
extension authors start working on making sure their extensions work
with the upcoming PostgreSQL version. Catalog changes and feature
reverts can still happen at that time, but should be rare and we
would like to hear from extensions about potential problems as early
as possible. Ideally, extensions should be ready by the time of the
beta2 release (scheduled for August), so packagers can prepare
extension packages to be released along with the final rc and GA
releases (September).

However, I am not sure where exactly to put that information. The
release-XX.sgml files are pretty volatile, and the beta information
gets removed for the .0 release.

Maybe under https://www.postgresql.org/developer/roadmap/ ?
Is there a general description of the development cycle that I have
missed?

Christoph