I don't expect to see widespread adoption in other areas though, such as cellular phones and similar. To my ears, I doubt the codec will compete with common voice intelligibility metrics, such as Diagnostic Rhyme Test [1] or PESQ [2].
However, it may be an improvement over SSB voice intelligibility!
I worked on Opus, which bottoms out at around 6000 b/s. A typical IP+UDP+RTP packet has 40 bytes of headers, which with 40 ms frames is 8000 b/s of overhead. Cell networks will use header compression to reduce that, but even so. 8000 b/s is almost eleven and a half 700C codec2 streams.
codec2 is just in another league. It's seriously impressive work.
I think a better metric is spectral power for equal intelligibility. Over an HF channel, given 2700 Hz bandwidth (nominal for SSB, although you can go narrower), and a given level of transmitter power, say 100W PEP on the SSB side, then take 100W PEP and whatever error-correcting modem you can come up with that fits in 2700 HZ on the digital side, what does it sound like? What is the intelligibility comparison?
There are a lot of factors in play here, BER, power level, channel fading, etc. It's not clear to me that a system that is good when it works but suffers total drop outs if it loses bits is better than an analog system that suffers noise floor variations but at least gives you something.
There have been some examples showing that for older versions of the codec running at twice this rate.
RE: fading, there isn't really any great way to fix that short of higher delays (longer FEC) or increasing bandwidth to be wider than the fade-- no other way around the signal not just being there.