It still feels fairly pyramid-schemey. "Purchase now, with expectation of return if others purchase in the future"

I think it's an unfair comparison only because they make it clear that a "pledge" is to support development of the game. Like getting a keychain from a patreon artist.

But it's ultimately unprecedented, and we are all learning as we go. I doubt there will be a crowd funded game like this again for a while.

AFAIK they actually stated that they could complete it without any more funding.