I know what you are trying to do....I would just paint the brackets the same color as the wall...they will not show very much. I am guessing the skim coat would crack with the movement of the shelves. I would check with your local big box store and ask them this question. Or a local cabinet maker...either one.

Haven't done it but don't see why it wouldn't work. If the brackets are heavy enough and you have one of the heavy screws near the bend of the 'L', there shouldn't be much (if any) movement, especially since you're attaching directly to the stud vs on top of drywall.

In the past, DS installed the lightweight floating shelves and the drywall always ended up allowing movement around the bracket. Guess who ended up doing the repair work!

If you can use thick enough steel rods you can sink them into the studs and into the back edge of the shelves.

A lot depends on how much weight you want to hold up.

Thanks for all your advice!