what remains

Amplifier circuit topologies haven't changed much since the 1970's not to mention there is a finite number of ways of arranging semiconductors to provide audio amplification and this is well understood and ultimately derived from the underlining technology of the day.
 
We should host a game show like "Wheel of fortune", only instead of letters missing from a phrase, have an amplifier schematic with just an input device and a pair of outputs.

"Contestants" would then fill in-between these with whatever circuit topologies they can imagine! Or guess at a particular spot "Gimmee a constant current source!" Ehhhhhhh! Next!
 
With continued improvements in the manufacture of transistors (lowering of junction capacitance
an increased HF response, lowering the input to output delay) we may be able to apply techniques
that were impossible to achieve in the past to improve performance.