but there's a big challenge with trust.

The idea is to be less of a trust-challenge than the existing status quo. My perception is that the current barrier is so high that there is no flow in the economy. It seems to me that @the-gorilla is one of the more active and well-connected people in the community and it was still a significant lift for his proposal to get approved. I figure that someone like me would have zero shot in the current system.

... so the developer ...

Since the DAO can be used for any project I think we should be careful to not get too locked in on the idea that it's only for developers.

gets a certain amount up-front and then additional advances are only paid after promised deliveries are met.

This is kind of how the proposal system already works -- it's paid out on a regular interval, but the big lift is getting it approved and then proposal voters mostly seem to have a set-it-and-forget-it attitude. In my mind the "lump sum" wasn't the key element of what I was suggesting, it's that the payment creates a floor to shield the creator from the unpredictability of the "per product" rewards.