rebase: allow non-head rebase-set when obsolete is enabled Obsolescence markers can represent this situation just fine. Rebased revisions are marked as precursors of the ones create by rebase. Unrebased descendants becomes "unstable". If obsolescence is not enabled we keep the current behavior of aborting. This new behavior only applies when obsolete is enabled and is subject to future discussion and changes.

amend: allow amend of non-head when obsolete is enabled Obsolescence marker can represent this situation just fine. The old version is marked as precursor of the new changeset. All its descendants become "unstable". If obsolescence is not enabled we keep the current behavior of aborting. This new behavior only applies when obsolete is enabled and is subject to future discussion and changes.