According to the post below the construct 3 storyboard splash feature should work correctly. You can access this by opening the icons folder and adding your preferred images for foreground, background and storyboard splash, and assigning them the correct role in the properties viewer.
The Splashscreen feature (Storyboard), now works well now in Construct 3, on the latest update.
The Adaptive Icons (Foreground + Background) was working all this time, at first it looked broken to me since it somewhat didn't scale like Android Studio.
To make it scale in Construct 3, you need to match the size of both Foreground and Background. And, most especially, include the transparent areas to avoid it stretching.
It doesn't have Android Studio icon tools, but I think this is already enough for most apps, and adds simplicity.