Although anyone can self-publish today, and many do and make an excellent living doing so, the publishing side of it is very different than the writing side.
Create a publishing house that specializes in self-publishing authors. Instead of the two current options – do it all yourself or give it all to the publisher – this publishing house is in between these options. It cooperates with the author and shares the work and duties, contributing the unique expertise needed like marketing, editing, etc., and also shares the income generated by the cooperation.
Writing a book even a good one does not guarantee it will sell. Knowing how to sell and promote the book, launch it and use all the right tools in the right way is a different expertise.
Have a marketing agency with the specific working framework for self-published authors.