However, experts say there’s a reason Congress hasn’t made such a change already. It would be complicated, not to mention enormously costly to the federal government, to enact. It would encourage many higher-paid workers to restructure their compensation to classify some of it as “tips” and thereby avoid taxes. And, in the end, it likely wouldn’t help millions of low-income workers. “There’s no way that it wouldn’t be a mess,” said James Hines Jr., a professor of law and economics and the research director of the Office of Tax Policy Research at the University of Michigan’s Ross School of Busi…