This is where it gets cludgy in the existing marketplace version, I’m afraid. How it WILL work for inheriting UI_Dialogue_TextItem in the next version is similar to inheriting from UI_Dialogue, where you override the ‘GetTextControl’ and provide your own. With what you have now, you will need to change the base UI_Dialogue_TextItem class to have this getter for all references to the txtText widget. (Most, if not all of these references reside in the one widget, so it’s not too damaging).
A small note is that if/when you update to the newer version (once it’s available), you may have to fix your inherited widgets to call the new GetTextControl function.
Hope this helps!