All good ideas, as I said, but it isn't realistic. Sure, it is possible and probably would be very popular, but it isn't going to happen anytime soon. Also impedance matching is a joke with speakers. You have 4, 8, 16 ohm speakers. Not many different designs going on in the speaker world. Most of them use the same impedance (yes, there are exceptions), most consumer grade speakers are those configurations, thus making amping, preamping, etc. pretty easy and streamlined.
It's not going to happen, but if you guys wanted true impedence matching (or removing impedence from the equation), a current driven analog output circuit, such as a Darlington transistor, would be ideal for single driver speakers such as headphones. Then it wouldn't matter what impedence your headphones were, only the amplifier gain.