With an optimized mobile application, that will make it to where my wife can use the software - so that is mandatory.
Scheduled transactions, import ofx, and payee management will be required for me to effectively use the software. My workflow relies heavily on using scheduled transactions as bill pay reminders, and then I use the import ofx capabilities to clear transactions, and you can't have importing without payee management if you want meaningful payee names.
Those three are what it would take for me to bury YNAB4 and move forward at this point.
After that, search capabilities and running balance are high on my list. I can function without them, and I would switch over before they were available.
Lastly, goals. I can do everything I need related to goals, but it is something that would be nice to have at some point in the future.