I often encounter the argument that quantum mechanics reduces to classical mechanics at sufficiently big scales, as soon as h becomes sufficiently small respect to the actions involved. I clearly understand this for the uncertainty relations.
But when it comes to superposition, what is preventing it to happen at any scale? Is there actually something that prevents superposition for system bigger (in spatial or any other dimension) than some threshold?
As a practical example, is there an insuperable limit in how many q-bits we can have in entanglement?