I'm not sure that giving the money to charity would necessarily weaken the incentive. I get where you are coming from, but there is a whole lot more to motivational psychology that that. In the big picture, having an accountability partner (which you do have—"supervisor") is probably a bigger part of the motivational aspect.
I feel like it would make more sense to give the money to the supervisor than to "GFDI itself". Maybe you'd take a cut or something.
I just can't imagine people wanting to signup for something that would potentially give the money to some random website. Sure, people would be motivated to accomplish their goal so that the money doesn't go to GFDI, but I think people would be equally motivated to just not use the product at all.
If you fail to reach your goal, the amount goes to GFDI itself. It could go to a charity or third person but that would make the incentive to finish your goal weaker. Since it's a startup and the goal is to make it profitable as fast as possible, that's the business model.
I saw this and thought "It's Gym Pact for the rest of your life." Key difference is that Gym Pact funds the people who achieve their goals from the money they collect from people who fail.
Delphi
eu/acc: European Accelerationism
The Matt & Adam Show [Ep. 9] Aaron White - The Unicorn Wrangler