iOS should let apps other than Apple's to have persistent notifications.
Reminders, Calendars etc are the only few apps which can have persistent notifications. No other app is allowed. I don't know why apple can't put it behind a permission. There are plenty of productivity apps like Todoist, Fantastical, Evernote which will benefit from this.
The first party apps are sufficient for a lot of people and the needs of the rest can be fulfilled by the plethora of options in the app store. Why deprive this group of their productivity workflows?