[AndrewBissell]

This is a really intriguing idea! You would of course run into the issue that that product would appear to have horrible returns right up until the rug gets pulled out, and liquidity might be an issue (margin for the short would have to be provided and presumably could not be directly provided by the long positions). But at the very least one could theoretically write something which could take in a portfolio of ETF positions and output "short this much ABC and XYZ to be net flat in those stocks."