Apple has at long last answered the hopes and dreams of people hoping for mouse support on iPad. With the new iPadOS, you'll be able to hook up a USB mouse or the likes of Apple's Magic Trackpad, as iOS developer Steve Troughton-Smith discovered once the developer beta went live.
— Steve Troughton-Smith (@stroughtonsmith) June 3, 2019
At least for the time being, mouse support is available as an AssistiveTouch accessibility feature. It's not clear as yet whether the OS supports Bluetooth mice, though there seems to be a Bluetooth devices section in the Pointing Devices settings. The cursor looks like a large circle in Troughton-Smith's video, but there's a menu for cursor options in the clip too.
It's a welcome move not just from an accessibility standpoint, but also for those who use their iPads for work or creating, and might get work done faster with a mouse than with touch inputs or Apple Pencil. Hopefully, this is a precursor to broader mouse support on iPad. Combined with iPadOS and external storage options like thumb drives and SD cards, it seems iPads are about to become more useful than ever.