Google recently announced the beta version of Android 8.1 with tons of new features and enhancements for Pixel and Nexus devices. However, there's no information whether Motorola will update the Moto G5 Plus to Android 8.1.
Watch: Android 8.1 New Features!!!
But you can Install it right now via Pixel Experience ROM. Developer "jhenrique09" has successfully ported Android 8.1 Oreo based Custom ROM for the Moto G5 Plus. Additionally, most major aspects of the phone are working as expected (such as RIL, WiFi, Bluetooth, etc.).
With Android 8.1 Oreo, you'll get new Wallpaper Themes, Pixel 2 Launcher, Redesigned Power Menu, new Shutdown and Reboot Animation, Round Statusbar Icons, and Settings.
You'll need to Unlock Bootloader and Install TWRP Custom Recovery in-order to Install the Pixel Experience ROM based on Android 8.1 Oreo on Moto G5 Plus Potter. You can grab the Custom Rom ZIP file from below.