Green’s Dictionary of Slang

(orig. US) an ironic intensive placed at the end of a sentence.

1936		Sat. Eve. Post 19 Dec. 11/3: ‘The only kinda men I want are ones who wouldn’t be afraid to try out for Whiteman.’ ‘Whiteman yet!’ scoffed one.
1943		M. Shulman Barefoot Boy with Cheek 66: ‘We finally got a story into the paper. Not just a little story, but a big story, and on the front page and with pictures.’ There were admiring whistles and cries of ‘Pictures, yet!’ from the audience .
1952		W.R. Burnett Little Men, Big World 7: Sarah, noted for jumping the gun, was already talking about sending the oldest girl to private school. Private school yet!
1963		in T.I. Rubin Sweet Daddy 66: A shyster yet with a rep.