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

  I agree with you unsound, class D has come a long way in the last few years,  I have purchased 2 digital amp company amps and his amps just keep getting better

Yeah, but class D amps are just attempting to solve a problem unrelated to sound, namely, power consumption. Not everyone wants a big class A amp that runs as hot as a toaster. The problem of flat, low distortion amplification has pretty much been solved in a variety of ways which wasn't so much the case 40 years ago. Back then even solid state watts were pretty expensive. 
I never expect to own a class D amp. I've got a healthy Pass F5 clone belting out about 37 watts RMS and it's probably the best sounding amp I've ever heard. I'm not at all bothered by the fact it runs as hot as a pot of coffee. 

Call Underwood hi fi..big stuff coming out early next year. 

Class D is second rate sound quality, not in SOTA league at all!

Class D is on the cusp of breaking out into SOTA performance.  There are a very few very expensive Class D's that can really strut...most are very far away.  I remember when CD players were awful....now, there are some excellent ones.