Going through the IPR process will cost half a million and a year of time at least. The filing fees alone are in the tens of thousands. It's unlikely anyone would pursue a case unless thought they had a good chance of winning. Kyle Bass's strategy was just to hope that filing the patent dispute would cause the share price of the manufacturer to decline, which it did not in many cases. He ultimately lost most of the time in court, so I don't know how much he actually profited.

Have you heard of Cloudflare's Project Jengo [0] [1]? They were sued by Sable, a patent troll. So they made a website where anyone could submit prior art for any of Sable's patents and they would pay I think around $1000-2000 if it helped their case. Imagine if you had a website where you listed drugs alongside their patents, and a bounty in dollars if you found prior art. The bounty could be funded by hedge funds, generics companies, or other competitors. If the submissions were solid enough, they would take the case to lawyers and hopefully win.

    KEYTRUDA® (pembrolizumab)
    - Bounty: $100,000 
    - Patents:
        - U.S. Patent No. 8,354,509
        - U.S. Patent No. 8,900,587
        - U.S. Patent No. 9,834,605
        - U.S. Patent No. 11,117,961
        - U.S. Patent No. 9,220,776

    ...

You would probably need a lot of connections to make this work. You would also basically create a side hustle for bored patent lawyers or people with a lot of time on their hands. Though the people who are really good at this sort of work probably already make a lot of money, so maybe it wouldn't work.

This is basically your original idea, but there's a monetary incentive. I don't think people with the level of expertise needed to do this would do it for free.

[0] https://www.cloudflare.com/jengo/sable-prior-art-search/

[1] https://blog.cloudflare.com/the-project-jengo-saga-how-cloud...

Edit: but maybe I'm wrong. The CEO of Cloudflare says most of the people who submitted probably would have done it for free: https://news.ycombinator.com/item?id=41732580. But then again, Cloudflare was able to publicize their cause easily among technical people who can understand software patents on places like HN, and there was a moral righteousness element to it because patent trolls are parasites. It might be difficult to inspire the same level of enthusiasm about orphan drugs, and there is also likely a smaller number of people who have the skill to review drug patents.