Include the same customization capability that has always been in SharePoint search.
For years we have had the ability to successfully customize SharePoint search with managed properties, crawl rules, query rules, result sources, it goes on and on. With MS Search you have taken that flexibility away. So now half of our tenant gets one search experience and the other half (Modern sites) get what they get. Put the two together with full functionality or give us an option to use classic search in Modern sites. It's getting really frustrating explaining to users that a Best Bet is now a Promoted Result or it could be a Bookmark depending on where you are. It's all the same thing!