That's not the way patent trolling works. Normally the troll buys a portfolio of existing patents, then waits for someone with deep pockets to infringe. It's usually the victim who tries to argue that the invention predates the patent.

I can't see it helping the little guy, because if one party has infinitely deep pockets and the other can't afford to fight anything in court, then the larger party can lawyer up and beat the little guy into submission regardless of what the law says.