I've reviewed the changes that we've made and I've come up with this analysis. I suggest that a starting point would be to take the current TinyMCE code and re-apply the important features to it. Then look at the bug-fix items and see which ones haven't been fixed in the lateste TinyMCE.
I would recommend that we then submit our changes to the TinyMCE core as a patch, so that they have it in their codebase.
* Manual placement of toolbar location, and blur/focus handlers on the controls to facillitate this.
* Add macrons to insert character
* Added formElement.isChanged() method, to help with SS change detection
* Added image class field to image properties form
* Changed default with to 600px, not 320.
* Begun adding support for strict XHTML content-type header (nbsp = #160 and case-insensitive tagname checking)
* Fixed positioning of context menu when scrolling, and to prevent it from showing off the bottom of the screen.
* Got the editor to respect the <base> tag
* Bug fix in table editor
* Bugfix in inserting the typography stylesheet
* Made area_width and area_height parameters instance specific, rather than global (not actually needed anymore)
* Fixed support for # directive in valid_elements config optin
* Fixed auto-resizing editors
* Fixed isDirty(), although not completely