That's unfortunate, but understandable. It's a big shift.
I've worked on this separate from SweetHome3D, but I think it should be possible to have something similar in SweetHome3DJS: https://github.com/bobvanderlinden/sweethomewebxr/ It works with an exported OBJ file. You can see the result here: https://bobvanderlinden.github.io/sweethomewebxr/
I've been working on a webxr viewer for an (OBJ) export of my SweetHome3D. You can find the project here: https://github.com/bobvanderlinden/sweethomewebxr/ It is hosted here: https://bobvanderlinden.github.io/sweethomewebxr/ I confirmed it works on Quest 2 and Apple Vision Pro.
I love this software and I see a lot of potential for the JS version. I wish it was more well-known and got more outside contributions. It's hard to say for sure whether GitHub would help, but for me personally it would. It has taken me quite a while to find that there was a feature request section on the site 😅