There’s no way for an Extension to automatically pull in other Extensions. This would have to be a manually developed Extension i.e. someone builds an Extension with the specific features from other Extensions.
Is there any particular overlay functionality you were expecting to see in a single overlay or were you hoping to see the full suite of overlays be usable together?
Unfortunately, it’s seems a pretty purposeful decision to not allow multiple overlays at once. It’s possibly something that will change at a later date, but I can see the problems this could easily open up unless the overlays are designed specifically to not conflict.