You're completely correct that it was going to be NPV neutral and an endowment. But the structural independence that ISOC would then have had, and the freedom from constraints of income tied to a service delivery changes how you plan and what kind of long-term plans you can make.
So I sort-of agree and disagree. It wasn't really a huge windfall outcome, viewed as a perpetuating fund. But it was a huge structural change for ISOC, and very possibly the IETF too.
I think you're right to suggest the actual income from PIR was predictable. But it was also unusual. Deriving so much money from a single place imperils tax status as a 501(c) I am told. perhaps this wasn't a problem for them. (I've never been aware of the board and its finance decisions)
I was led to believe moving to a trust with oversight of a fund is different, and more beneficial as a perpetuating entity. And, Org and PIR relates to the status of Verisign and COM and also places ISOC in a relationship with ICANN which I suspect was irksome, because in so many other senses ISOC felt it was not subject to ICANN direction but actually one of the peer-set.
If I had been on the board, and a well structured proposal had been put to me to do this, I truly don't know what I would have said. My instinct is: this should be discussed publicly and we should get community consensus, but I could imagine other pressures/tensions emerged.
So I sort-of agree and disagree. It wasn't really a huge windfall outcome, viewed as a perpetuating fund. But it was a huge structural change for ISOC, and very possibly the IETF too.