Are music servers the future?

You could be just as well talking about:
Stereo recording
Solid state amps
Quadraphonic records
8 Track tape
Cassette tape
Digital FM
Etc.

Only time will tell.

Mapman, no I don't have any figures, Stereophile, if I recall does have figures about its growth. I am reconciled to realize that modern culture has passed me by. I cannot stand most modern music. I deliberately did not quantify my statement.

I am listening now to double DSD from my server. Of course listening to 44.1 at double DSD upsampling moves the filter dramatically upward revealing much heretofore unheard realism. And SACDs if they are real upgrades, are outstanding.

I'm streaming my .wav files at home to my PC at work using plex configured for highest sound quality and listening on klipsch s4 earbuds. Sounds damn good!

I listen to the same files on my "big" system at home via Squeezebox to my DAC of choice. This is the bomb!

Still like records as well, especially older titles that are high quality excellent analog recordings. Those are always a special sonic treat. Not as much many records made in the 70's and newer. Mediocrity started to set in on a large scale there as well. Good modern digital streaming is much more consistent overall, even if the nth degree of technical perfection in terms of resolution is still out there still on the horizon somewhere.

I do hear new things on some recordings that are hard to detect otherwise in any case, even listening at work on those inexpensive but good qualty ear buds hooked to my standard-issue PC

You remind me of my grandson listening to Pink Floyd on ear buds. I took him up to my listening room and played the vinyl version. His comment was it doesn't sound like the same recording. But for his convenience he went back to listening to the ear buds. You can lead a horse to water but you cannot make him drink.

I'd guess that servers are the future but I've been hearing that for quite a while now and progress towards that future seems very slow.

Sony, one of the three major music groups, has their first servers out now and promises lots of high res downloads. Sony says the other two majors, Universal and Warner, are on board too. So maybe things will start happening soon. I hope so.