That could become a terrible disadvantage for Facebook and could be weaponized by competitors - unless it is mandatory for all companies publishing ads online (and maybe offline?).
Yeah for it to work it would have to be a regulation for all companies that allowed targeted advertising and reach a certain scale.
I don't think it is necessarily true that consumers would prefer a social network with non-transparent ads over a social network with transparent ad funding. Making ads transparent might even help facebook's bottom line by building more trust with its users.