The referenced email suggests how both needs (support URL space, and easy committer access) can be satisfied at once. So why deprecate http://apache.org/forrest/*
in favour of http://xml.apache.org/forrest?
What happens if Forrest becomes a TLP? Deprecate http://xml.apache.org
and switch to http://forrest.apache.org?
This perfectly illustrates why the original URI was chosen, namely to eliminate as much as possible that may change in future. It is primarily an identifier, and secondarily a locator.
Please read through www.w3.org/Provider/Style/URI,
repent, and let us never speak again about breaking URL contracts again ;)