Unfortunately, editable metadata still doesn't exist, but is scheduled for 3.0. A
roadmap is here. (Note that a revamped upload was pulled ahead and released in 2.6.)
Version 3.0 will include a client template feature where much of the UI is built from HTML templates. These templates will support jQuery template syntax (or, more probably, the recently announced *replacement* for jQuery templates). I have an internal build with this working but I have ignored displaying the metadata for now.
Handling the editable metadata involves building a new UI mechanism, as the old system uses ComponentArt Dialog and Grid controls. All I really know at this point is that is will be javascript based (jQuery, templates, web service callbacks) instead of ASP.NET server controls. But I haven't worked out the user workflow or UI design, so if you want to get involved I welcome your help. I imagine the underlying business and data layers will remain mostly unchanged (they already support CRUD operations against the media object metadata table).
Roger Martin
Creator and Lead Developer of Gallery Server Pro