After 2 years and a computer failure, I and some other people have managed to put our 2023 attempt at extending the SoundFont specification into an actual and proper specification, called SFe, available here:
https://github.com/SFe-Team-was-taken/S ... es/tag/4.0
We have Polyphone's developer, as well as other player developers, in on this.
We have also resurrected Silicon SoundFonts (Section 11 of the SoundFont spec, which is an official SF2-to-ROMpler mode, and I've documented it with a reference implementation here: https://github.com/stgiga/siliconsfe/tree/main and it's factored in to our new spec.)
We are even in talks with Fluidsynth on the matter, hence why I'm approaching VLC about this. I ALSO have some contributions to make for the captioning, namely having UnifontEX (https://stgiga.github.io/UnifontEX available for use as a fallback font for captions, due to its high Unicode support.
Basically, I and some fellow developers are trying to make media players better.