This is very interesting. At least around here, ARES is struggling with what to adopt for digital use. There are so many 'standards' out there.
I don't want to talk out of school, but NTS has selected 'Winlink Classic' for it's standard for the NTS-D system. I think this may be an unfortunate choice for several reasons. Winlink systems can be set up to be 'radio only' but that's not the typical solution.
ARES teams around the country are adopting the NBEMS suite of programs, which run on top of FLDIGI, on many different protocols. MT-63/2000 is gaining popularity on VHF FM, and Olivia 16/500 or 8/500 on HF. The MT-63/2K works well with 'acoustic coupling' - eliminating the need for a soundcard interface. There is a smartphone app that could be used to send and receive MT-63/2K traffic over an HT or mobile rig.
Army MARS here has a PSKMail server in place. This program also runs on top of FLDIGI, so it's compatible with NBEMS, while providing many of the email capabilities of WL2K. Right now, there are number of people around the country doing NBEMS on 14065, 7065, and 3583.5 (USB - audio center frequency 1000 or 1500 Hz +/- QRM). It would be great if NTS-D would establish servers so NBEMS users could send NTS messages any time they can.