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

I see two things improving these days, DACs and class D power amps.

Other than incorporating new, more capable DAC chipsets into new preamp models, I agree with others who have posted here, that the preamp itself isn't really improving.  In my case, I have never used the DAC in my preamp, I went with an external unit, one based on an FPGA chip, where firmware updates improve the performance of the DAC, like getting a "new" unit every year or so!

I must admit that it's been years since I auditioned a class D power amp, and back in the day, was not impressed with the sound (to me it sounded "brittle").  With all the new class D designs, eventually I'll take the time to update my experience with class D and audition some of the new amps.

The problem with most DACs is not the chipset on the front-end.
It is the analog stage that follows. The digital data to be converted to analog far out strips the ability of the analog section to pass along the stored image.

" the preamp itself isn't really improving "
This was true up until now.

The digital data to be converted to analog far out strips the ability of the analog section to pass along the stored image.

This statement is false.

My point was that unless you attach a distortion-less analog stage to the back end, the full resolution cannot be realized.

I can run a 16 bit dac that will out perform a 24 bit dac simply be using a distortion free (0%) analog stage.

In a DAC the analog stage is the weak link.

I'm assuming that you have used tube output stages and recognized the difference in sound quality.

^^The premise of the post above is false.

Try running an analog source through that output stage and you will see why.

As a bit of a tip: its probably not a good idea to talk about 'distortion-less' in the way that you do, it strains credulity.