Thanks for linking to this, here is my initial assessment of the situation:
(1) Your fix should work, but only if plone.app.contenttypes is installed (cannot import RichTextFieldWidget without). I'm just trying to use widgets 1.x without p.a.contenttypes. This could be modified to work around (conditional import and redefinition of RichTextFieldWidget factory function is simple enough).
(2) @thet's fix here does not accomplish the same thing as your fork, it only preserves status-quo functionality for Plone 4 (but widget configuration will not work). Things that are broken without the configuration that plone.app.widgets.dx.RichTextWidget is providing include: browsing links, browsing images, any button, plugin, or style configuration. What one gets here is a stock TinyMCE 4 that breaks in subtle ways.
(3) Upload through TinyMCE from static portlet is broken AFAICT no matter what (though I have not tested all permutations).
I think I may try to experiment building on what you put together here:
... I am hoping that a minor change here might allow me to use your fork without installing plone.app.contenttypes (so that plone.app.widgets 1.x will expose the factory for the widget). OTOH, I might just expose the widget factory in plone.app.widgets 1.x regardless of plone.app.contenttypes installation status.
I will update this thread once I come to some kind of workable conclusion.