I found out how to use the block states of fire. The block behaves a bit weird. If there is a block below the fire the client always uses value "0" for "age" state. But without a block below all 16 "age" states are recognized correctly by the client.

This means we can use fire for 16 different light emitting blocks: Laterns, chandelier, ...
Also fire connects to flammable materials which makes it possible to make oriented light sources like these:
It's a texture I found in Gondor pack at the Cocoa block. All three latern you see are fire blocks with "age": 1. The planks beside make them connect to that side.

So if you have an idea for better light sources using this. Submit your textures!!!

Particles can be made invisible. Not sure if it would be possible to change to smoke. I think the color is hard coded.

Sorry, I didn't explain properly.

I meant it is possible to make particles invisible by removing the corresponding parts of that particles file in the texturepack. Indeed we will remove the redstone particles in the URPS update. Redstone wire chains, moss and dirt patches would look very weird with redstone particles around

So you can make the particles invisible by removing them from the file or you can change the shape of them ofc. But the color of the particles is not defined in that file, so redstone particle smoke would still be red. Also I would expect that the particles will not support transparency which would be quite important for smoke.

Anyway good idea and good question. Keep thinking about resource pack stuff. Many things are possible, we just need to find them