There are things your new editor will not do. I cannot recreate the newsletter without tables or HTML. The old editor had a nice visual table creation tool. Your new editor does not nor can I use HTML to create tables or custom presentation. I cannot duplicate the newsletter in the new editor. We have switched to MailChimp and successfully recreated the newsletter with advanced features at much lower cost.
You are going to lose more of your users because of this dumb decision. The old editor is still active and I can use it to edit saved drafts so you only need to re-activate the copy function.
Your new editor is not a step forward but instead a step backward.