I like the idea of the OrderSupport-Mixin-class. But maybe we shouldn't introduce a new additional meta_type "Folder (Ordered)". Instead we should extend the normal Folder with OrderSupport as originally proposed. People who don't need order support don't have to use it. All other people can use the OrderSupport without converting their Folder-(or-derived)-Instances.
FWIW, if "ordered folder" functionality needs to go into the core (which I'm admittedly leery of to start with), I think I agree with Maik, as long as: - the ordering method names are sufficiently verbose (to reduce the chance of acquisition name collisions). - the default Folder ZMI UI does not change, but can be influenced by add-in product code. FWIW, this whole business would be made much easier if we moved the skin machinery out of CMF and into the core. - C