This is an intriguing idea, but I think it would have a big marketing problem. Most of the people who are at risk of being sued by a patent troll aren't aware of that risk, or so I imagine. Maybe that's changing as the problem gets more press, but I still think the necessary outreach would be difficult.
Lawyers specialising in handling IP cases would probably have an interest in such a service though; potentially far more work for them than agreeing with the client that settling probably is the cheapest option. Insurers underwriting intellectual property liability insurance (it exists!) also have a very strong incentive to encourage, or even require their clients to use such a service.
And for some non-software industries many firms might have a pretty good idea which competitors/suppliers/clients of theirs are likely to be threatened by the same patent.
