I don't know if this is within the scope of the project, but it would be pretty darn cool.
Iris is a mod that allows shaders to be run in fabric without Optifine and can work with sodium.
using Iris and Iris's fork of sodium there are issues.

I used CTM (connected textures mod) and bits and chisels to test, and CTM didn't connect textures, and bits and chisels crashes the game.

Here's a video of me demonstrating
youtube link

Here is a 7zip of the mods used:
google drive link

Minecraft 1.16.5
Fabric 0.11.1
Fabric API 0.30.0

If I remember correctly, Iris's fork of Sodium is too old to work with Indium currently. You can merge them yourself (I think someone in the Iris discord has?) but I won't be doing that myself, it's up to coderbot to update the fork.

Note that the outline rendering doesn't require the Fabric Rendering API to work - the game just crashes when Indium tries to render the Bits and Chisels block in the world. CTMF doesn't come with a built in resource pack either, you'll need to download one (such as https://www.curseforge.com/minecraft/texture-packs/mc-connected-ctm) for it to actually do anything.

Well, dang you're right. Thanks for the feedback.

Is this possible yet?

If I remember correctly, Iris's fork of Sodium is too old to work with Indium currently. You can merge them yourself (I think someone in the Iris discord has?) but I won't be doing that myself, it's up to coderbot to update the fork.

The fork just got updated btw. https://github.com/IrisShaders/sodium-fabric