In one sense, this suggestion is as good or better than any I've heard. Let the defendant raise the possible issue with a judge - let a (presumably impartial and intelligent) judge look at it on a case-by-case basis, and let the plaintiff know in selected cases "this one's going to cost you lots if you lose". I guess there's then be a danger of a "reverse class action" thing, where someone like the scan-to-email patent holder sends out hundreds or thousands of legal threats, and some law firm decides to try and run up half million dollar costs for each and every defendant.