There is a working patch which makes existing TinyMCE 3 editor profiles work with TinyMCE 4, but a lot of settings have changed between the editor versions so there's no guaranteed "upgrade path".
Users applying the patch but deciding to stay with TinyMCE 3 should notice no difference. Upgrading to TinyMCE 4, testing the editor without saving an editor profile, and then downgrading back to TinyMCE 3, will not alter existing editor profiles or the editor behavior in any way.
Downgrading saved profiles, or profiles created after TinyMCE 4 was installed, is not supported. Downgrading to TinyMCE 3 again and creating new profiles still works as expected.
Note that any settings dropped in TinyMCE 4 will be lost if saving a TinyMCE 3 profile after TinyMCE 4 has been installed.
The value for TinyMCE 4-specific settings may not actually be stored in the profile yet, even though they show up with a default value in the profile editing GUI. but the default values should match what the editor uses as its defaults when no value is explicitly set.
The patch is built for Wysiwyg 7.x-2.x, but the editor implementations in Wysiwyg 6.x-2.x are very similar so the patch should apply there too with minimal changes. Please go ahead and test this if you feel like it, but report problems with the 7.x-2.x patch to prevent a situation where bugfixes have to be applied to two different patches on each reroll and potentially allowing the versions to drift apart. A final backport of the 7.x-2.x patch will be created for 6.x-2.x once it's ready for commit.
Compile a list of settings supported by Wysiwyg for TinyMCE 3 and find their equivalents in TinyMCE 4.
Paste [from Word] settings will be dealt with in another issue once this is done.
Compile a list of issues we absolutely need to provide GUI widgets for out of the box. More can always be added later.
Compile a list of features/settings/plugins/buttons which had to be dropped or could not be cleanly migrated when loading a TinyMCE 3 profile when TinyMCE 4 is installed.
Make sure all TinyMCE 4.0+ changes have been accounted for, if needed.
I always forget something here....
tinymce/js/tinymce/tinymce.min.js, or you could probably also use the non-minified version which probably has a different filename.