Action Launcher v28, which is currently on its second beta as I write this, now officially supports Android Oreo's Adaptive Icons feature, which has eluded third-party launchers until now.
Adaptive Icons are a new feature in Android 8.0 that allow app developers to create home screen icons of various shapes to suit manufacturer preferences and, in the case of themers, icon packs. From developer Chris Lacy's blog:
Pick from 5 Adaptive Icon styles: circle, square, rounded square, teardrop and squircle.
This update also sees big enhancements to Quickedit, Action Launcher's powerful icon editing system which offers suggestions for icon replacements based on icon packs on your device. Adaptive Icon support is now integrated into Quickedit, so you can quickly pick the icon shape that best suits your mood.
Prior to installing, you'll need to opt into the Action Launcher beta, which can be found at this link. Once you've opted into the beta program, the update will download as normal from the Play Store.