Are future improvements in Amp/PreAmps slowing to a crawl?

I'm sorry. I'm just not buying this. I'm sitting here listening to an amp that's flat -.0dB DC to -.25dB@500kHz and will produce text book perfect square waves to 200kHz. And it does it in P-P class A. I'm no engineer, but I'm pretty sure there are zero speakers that could exploit what your claiming.
I feel like the speaker question is the one being forgot here. I built the amp I built because after careful consideration it was probably the best fit for my Focals. Are the F4 and J2 great amps? Oh yes! But probably not with these speakers. The only amp that will always output a perfect signal is the one with absolutely no damping factor.... And it'll sound lousy. If your speakers are extremely benign, well, you're probably going to be a huge fan of SET's. If you're running speakers that are going to draw current from the amp way out of phase with the signal and have impedance that's all over the graph, you want a muscular solid state amp that will grip those drivers with beefy damping. 
As it is, my F5 surprises even me after a long day with it's tactile conveyance and seemingly boundless stage. I'm pretty sure I'd be looking quite a while to best this thing. I honestly don't see how a zero feedback class AB amp could do it. 

hi @roger_paul 

I am utterly fascinated by what you have written. What you say is interesting insofar as comparatively I recall going to a talk by Nordost and Vertex cables when they explained that they looked at sonar technology in designing cables which has not been done before - likewise LAvardin make their designs to get rid of 'memory' in solid state circuits.
I look forward to how this develops and if you/colleagues will make such a design available for jo-public.

So Roger, have you quantified this axis then?

That is the question I asked before and got a long answer that seemed to contain neither yes or no. Have you quantified, do you have a spec for this circuit?

The spec for the velocity along the horizontal (time domain) axis = constant

Amplifiers that do not control this property are not constant (unstable) and as a result have varying degrees of smear or focus issues based on microscopic time warps.

Ok here is the answer to the age old question "why do tube amps sound better even though they have higher THD?"

Tube amps sound amazing because the velocity variations are minimized. I knew this back in 1969 when I use to design tube amps.
It is why they are still hard to beat.

But - they are still unstable. Removing the variations completely gives you an amp that has no sound of its own. IOW it does not sound like tubes or solid state.

It "sounds" like air.