Apple planning Luna Display-like desktop extension feature for macOS 10.15, codenamed ‘Sidecar’ | 9to5Mac

Looks like I may need to find and charge my Apple Pencil...

"Previously, Astro HQ came up with a solution, Luna Display, that allows Mac users to use their iPad as an external display. There are many solutions on the market for that, but Luna Display has become the top one given that it’s a hardware product leveraging the power of the GPU so the experience is as seamless as possible.

Now, Apple is working on making that seamless experience native to the Mac. According to people familiar with the development of macOS 10.15 – the next major version of Apple’s desktop OS – the new system will have a feature that allows users to send any window of any app to an external display. The external display can be an actual external display connected to the Mac or even an iPad.
[...]
Users with an iPad that supports Apple Pencil will also be able to draw with the Pencil on iPad when it’s being used as an external display for the Mac, effectively turning the iPad into a Wacom-like tablet. Engineers are also working on options that will allow windows to be easily snapped to one side of the screen, similar to a feature that already exists on Windows." 

Apple planning Luna Display-like desktop extension feature for macOS 10.15, codenamed ‘Sidecar’ | 9to5Mac