You are right, there is two options to make a plastic aspheric element , first mold complete lens from plastic , second taking a glass lens and adhesive a plastic aspherical attachment on to glass lens. I use only Leica and Rollei cameras and when even Nikon cant compete with Leica with glass lenses, I bet nobody cant compete with plastic lenses.
I showed a way , if you experiment with one of designs , laser or water jet cutting or 3d printing is a way to have fun.
Additionally , if you add nanopowders like titanium dioxide to acrylic , you can have extreme refractive indexes like 4 or so.
But nanopowdered plastic thick products tends to crack , everyone Works on thin coatings.
There is also , film based lenses like zoneplates or so.
My best bet and greatest fun could be attach a plastic anamorphic attachments on to large format cameras or cine cameras or digital cine cameras. If holga sells 40 dollar lens , someone could sell to digital canon owners a anamorphic attachment.