Well a trust based system is easy enough to set up. How's this:
- Open a ticket describing the wanted feature
- I'll reply saying how much it would cost to get that feature implemented
- People who want that feature can add comments with the amount they are willing to pledge
- If/when the amount reaches the target, I'll add a comment saying I'm ready to implement the feature
- All the pledgers can then send donations with a comment indicating they're for the feature and once the total is achieved, I'll start working on the feature
The two sources of risk are:
1) All the pledgers don't actually donate once the total is reached. Then those that did will have their money in limbo
2) I don't implement a feature even after receiving all pledges.
This has the benefit that you dont risk your money until enough people have pledged.