The policy is named 'default' because it was intended to become the default two feature releases after the new email code became non-provisional (first: deprecate not specifying an explicit policy, next release make default the default policy and make the deprecation only cover compat32).  However, for various reasons that switchover did not happen (one big factor being my reduced time spent doing python development).  It can happen any time someone steps forward to guide it through the release process.