I think the income from the current and past years would be sufficient if we were to reach a high percent of settlements.
I understand your though concerning future revenue from the infringing products, however the entire market could be wiped out as a result of new innovations in the technology. With a stable product in a stable market the parties may be able to reach an agreement as to future revenue and include those dollars in the total settlement.
The alternative is to reach an agreement on a per unit basis and trust the infringer will provide accurate data on the sales activity. I have managed such transactions on the receiving end and had no problems.
Projecting the future revenue stream to include in the final settlement, I think is out of the question. Way too difficult.