Is USB audio dying?

It seems inevitable that USB audio will be replaced with TCP/IP network based audio, either WiFI or Ethernet NICs built into an endpoint/dac as a transport for the audio stream. I have a nice USB audio rig, DAC + USB NAA, but I cant help thinking that pure network based interfaces are a more elegant solution.

At the high end, Mytek has done this with the Manhattan and its network streaming card, as has BluSound with their BluOS products. Many other products are doing this in the more general consumer friendly space like Denon, Marantz, Yamaha, Pioneer etc.

Are there any inherent advantages to handing off audio to the dac via USB?
It makes sense from a practical standpoint to get rid of the separate network transport and USB bus.  I have a Raspberry Pi running piCorePlayer, and all it does is read the stream from LMS on the ethernet connection, decode it to PCM, and send it out the USB to the DAC.   A ridiculously trivial job even for the little RPi.

On the other hand, with a built-in network transport, you are limited to whatever kind of stream the device supports.
No it's alive and well and getting better. Elegance is subjective and not necessarily related to SQ. You'll find more info on other sites that specialize in digital audio.
Dying?  No.  But as with most interfaces, they change and get refined.  IP seems to be the future, and some of the best sounding digital sources currently use IP.

In my experience, our systems and installs continue(d) to use optical Toslink on most projects because we found there was less noise and drops than USB, most likely due to the elimination of the USB Bus (they get busy) and any EMI/RFI interference.

Most of our current designs and systems use IP.  For clients that appreciate the performance and are willing to cover the cost, a properly terminated and deployed fiber network can have audio benefits.  Some audio designers and integrators are afraid of fiber, but we love it and highly recommend a proper fiber network to anyone wanting the best performance out of their music system.

USB is not dying at all. Like others have said it is getting better. That said, putting Ethernet right in the DAC can eliminate the Ethernet to USB converter that many of us are using (sonore, sotm, etc). I still see the initial stages of audio over IP being as problematic as USB though. As DAC manufactures implement IP with little understanding of how the protocol works, sort of like we saw with USB when it first came out. 
My player/DAC/int amp (Naim) accepts Ethernet input  by patch cable from music server (with only server directly connected to router), and it is a most convenient connection. Even Supra CAT8 is inexpensive compared to all but generic USB. Sound quality isn’t degraded to my ears. 
Are there any inherent advantages to handing off audio to the dac via USB?
Asynchronous USB has the same advantage as Ethernet or Wi-Fi  - making internal DAC clock completely independent from computer clock.  In contrast S/Pdif transmission is prone to jitter, that DAC has to reduce, either by syncing (PLL) internal clock to average S/Pdif clock, or by use of asynchronous rate converter (my Benchmark DAC).

Ethernet seems to be the obvious solution for digital audio, but for some reason it is less popular than USB.

I have been testing the Network of my Music library on server and Raspi end points. I use the Allo DigiOne and SPDIF to the DAC. There is simply no comparison in SQ. Bit perfect digital beats USB direct from host to DAC. USB is riddled with noise that neither the Schiit Wyrd or iFi iPurifier2 could correct in direct comparison. We at Affordable Audiophile recommend the digital coax over the USB on any application. And we also endorse HFC magnetic adapters which will make any stereo sound like Audiophile quality.
I don't think it is dying but just evolving as it was never in the first place meant as a music carrier and when used with a good Dac and a really good reclocking device then it gets up to the standard of other connections.
Is USB audio dying?
one can only hope ..... 
too many inherent flaws . as implied above, USB is only good for convenience, not for SQ. the USB was chosen by DATA programmers, not audio programmers, to the the "universal" link to/from computers. it was driven by business decisions, NOT audio decisions.

stay away from USB, suggest ethernet or wifi as alternatives 

John Darko is great.  I did the same test with my Auralic Aries streamer.  Wifi sounds better to me, and is also recommended by Auralic.

I use a AQ Carbon USB between the streamer and my Vega DAC.  I've tried toslink, coax, Aes... USB sounds best by a far margin.  YMMV.
Here is Mr. Darko himself (very recently):

"No single audio reviewer gets to properly assess more than 1 or 2% of any particular product category in a single year. And with such a large pool of hardware to choose from, we’re often drawn to products we’re reasonably sure we will like. It’d be downright stupid of me to single out a review subject that didn’t, on paper at least, play to my own proclivities."

He clearly states that Auralic is the exception and that he DID NOT find a difference between WiFi and Ethernet for the Auralic.

We need to recognize this as a sample size of one. One reviewer. One component. One comparison.