There are a myriad of possible examples.

Could be a licensee has a pending public offering that will provide additional revenues from which they plan to pay the license fee. PDS might agree to a contingency based on that situation being completed for some of the fee.

Could be that a licensee is planning on launching an infringing product, but hasn't yet done so and may or may not do so ultimately, but negotiates fees for that product at the time of licensing.

etc. etc.

Essentially, the point is that the contingencies would need to be such that the exposure to both sides can be "fixed" at the time of settlement / license. A fluid and still very precarious IP litigation process which could go any number of ways, and with claims that could be constructed any number of ways by the judge, is just not likely. Nor is it really sound business strategy.