Apple still has plenty left in store for iOS 13 before moving on to iOS 14 (which we will likely hear about this summer at WWDC). A week after the release of iOS and iPadOS 13.3.1, it began beta-testing iOS 13.4. This point release brings several welcome new features.
Update 03/18/20: Apple has given iOS and iPadOS 13.4 an official release date of Tuesday, March 24. It will bring official mouse and trackpad support to all iPad models.