Having seen a working v3.6.5, I thought I'd have a go at adapting the integration for CKeditor version 4.
On first impression the new version seems to have substantially streamlined the process of activating the editor, and dramatically reducing the number of files and components that have to be loaded. It seems to be substantially optimised. Along the way they have changed the calling method names, and have changed the way options are passed to each instance of the editor.
I was making good progress in stripping out what I thought was no longer needed from form-field-procs.tcl, and I had the main CKEDITOR.replace('$ID') { $options }; going just fine, until I received an object undefined error right in the middle of a huge block of compressed javascript in the middle of ckeditor.js. At that point I realised I was in way over my head! How on earth do you debug an error like that!?
I'd happily put some time into doing this, but I think I'd need someone to walk me through the existing integration since there are still some bits that I am a little foggy about.
Regards
Richard