And that's for an IPR, which is the cheap route to invalidation! A similar proceeding in district court would be an order of magnitude higher, and that was much

And that's for an IPR, which is the cheap route to invalidation! A similar proceeding in district court would be an order of magnitude higher, and that was much more common before the introduction of IPRs and the PTAB in 2012. Now, the author is not exactly correct in that the IPR is the only route forward to invalidate a patent. Some other options include ex partes reexam and protest, which may have the potential to be a lower-cost option. In any event, having pertinent (according to the author) prior art cited in an IDS in the file wrapper could neuter a patent anyways, as any attempt to enforce or transfer it would be severely hampered by its presence. Even any attorney who would take a case to enforce it could potentially have ethics issues in taking the case if they believed the cited art to be invalidating. And no one would buy a patent with such a cloud over it, until all cited art is addressed in a contentious proceeding or in examination it's probably not going to be sold.