Federico Vittici and Steve Troughton-Smith are saying that iOS mouse support could be coming this year as an accessibility feature of iOS 13. Mr. Vittici mentioned it on the Connected podcast, while Mr. Smith confirmed the rumor via Twitter.
I personally don’t see the need for a mouse on a touch-oriented device. But I’m glad it will be optional, instead of a required component of iOS. Edit: 20190425: I take that back. I didn’t think of the scenario where many people can hook up an external monitor to their iPad. In that case, mouse support is perfect.