I doubt this fight will ever happen regardless because Silva would be slapping his boy Machida in the face if he came in and easily disposed of Rua. Silva has stated awhile back that this lhw division belongs to Machida.
He may play in the waters a bit but I dont think he would ever chase the title or even fight a guy that beats Machida. Its just not a good look on a personal level the match however would definitely be entertaining.
I give it to A.Silva not only because of his striking but his elusiveness, speed and balance which is often overlooked.