Substratum latest release "670" brings full Android O theming support. Users can now theme on API level 26 resources/Android O Developer Previews. The source code of the same is readily available for themers.
Along with Android O support, Substratum 670 brings "Dynamic Refresh Mode" which automatically refresh the list of themes installed without triggering a refresh by swiping down. The latest build also fix some errors and adds minor new features.
Android O Developer preview is available for the Nexus 5X, Nexus 6P, Nexus Player, Pixel, Pixel XL, Pixel C, Huawei Mate 9 and the official Android Emulator.