Public bricks are already a thing, in the game. You can load a save as public, and there's a script that lets you place any brick as public. They do exactly what you describe. It's just that any brick owned by ID 88888 (might be a few more eights in there) is public. That's why that is always in the "Clear Bricks menu" even though that ID has never logged in. So, any brick of any type can be public, as long as 88888 owns it. I believe you can also use an ownership-changing addon (I think that's what the brickgroup wand does?) to change the owner to 88888 and that makes things public as well.
