A lot of the most popular ideas here share a common theme: issues with the default WordPress editor. I recently decided that rather than complain about it (okay, in addition to complaining about it) I would adapt an existing plugin to work with WP 2.7.
If this problem could be addressed, I think that there would be a great deal more development of alternative editors (or at least a lower proportion of those that fall out of use because of WP version incompatibility).
Realistically, you don't even need a full-blown API. All that is needed is, say:
- Start with a blank form: textarea and save/submit buttons, etc
- Document the IDs, form, anything else relevant
- The default editor can still be kept the same, and from what I can tell would only need to be slightly re-written to work
- Allow the default editor to be completely disabled just like any other plugin, so that a knowledgeable user can disable EVERYTHING and end up with the blank textarea/buttons
- ...or, of course, so another editor plugin can find and take over the editor form without having to work around what's bundled in by default
Instead of anyone expecting WP to try and please everyone, WP can have a default editor they feel is fine and leave it at that. New users still get the default editor, but it becomes trivial to find and use a different editor, or easier to write one yourself.