Power integrations topswitch is already the best monolithic offline flyback controller in the world. What about making it even better as follows….make an equivalent of linkswitch buck controller which works from input voltages of 20V to 60V….then use it to provide a secondary 5v supply for the opto of a topswitch…….in doing so you dissipate less due to opto diode current when you have secondary voltages  around 48V (or higher).

Also, the 5v rail could be useful for other things like a micro etc etc.

So will Power integrations  make such a modified, low voltage  linkswitch?