A few yrs ago someone asked me this question and i mentioned Rigo. He laughed at me, suggesting i said something dumb. I'm no talent scout but going with Mayfield. Obviously not as talented as Rigo but he's going to be problem for anyone at 140. And in a way - Shiming. Don't think he will be elite but he will be a solid title holder which will exceed expectation since everyone is calling him a bum.
Shiming may win a fringe title, 'n make a bundle, but only if he stays in China. By no stretch of the imagination is he a pro. He's a stick-'n-run professional amateur.