The big issue is trust here.
You have to trust them to produce work that a 100k a year dev would. You have to trust them to "come to work everyday". Those that they would answer to, the investors and the community might not have the technical expertise to evaluate their work.
Thats why im leaning towards singular task completion funding.
You know what will be done, you know how much it will cost, how long it will take.
Yeah I prefer project/task based quoting. Especially since there is a lot of learning involved etc so just because people quote 30hours if they know what they need to know it would be less.
I also think there needs to be more separation of concerns when it comes to community work, ie the servers etc need to be their own thing and it needs to be mentioned how dependant they are on a specific stack. This allows budget cuts or superfluous requirements to be dropped.