What is the money-no-object theoretically ideal speaker design. Pure functionality!

In principle, what features would a perfect set of stereo speakers have? (and what amplification would they need?)

Coaxial drivers? Digital crossovers? Waveguides? With or without subwoofer? Cabinet materials? Ported vs sealed? How many watts of amplification?

There are lots of very expensive speakers with fancy designs, but what things objectively improve the acoustic output?