Debian already carries the davs2 decoder library and the xavs2 encoder, but it does not enable them in FFmpeg's libavcodec. There is no support for AVS3 on Sid as of today.
I don't think we will want to enable those in contribs FFmpeg either due to --enable-gpl. There is anyway not much point using libavcodec's non-native decoders, IMO.
On the bindings side:
There is an IEEE standard for the MP4 bindings.
It seems that AVS2 is already in Matroska specs, but AVS3 not?
I have no clue about TS and PS though the linked Github has bindings.
The linked Github disagrees with current VLC on the AVI bindings.
RTP bindings are supposedly specified by IEEE too, but not implemented in the linked patchset.
Given the license of the library I'm not sure why they need --enable-gpl, it may be due to use parts of x264 in the encoder. libdavs2 is GPL. The AVS3 decoder is BSD.
AFAIK, the github is enabling mutually exclusive FFmpeg options, as you can't have GPL and advertising clause together (unless you don't redistribute).