Unfortunately, averaging monthly donation doesn’t work in the real life. My educated guess is that getting 300 people to pay 20 euro a month will be some serious example of black magic at work.
If you can get 300 people to donate, 80% will be paying 2 to 5 euro, 15% smth like 10 euro, and then the last 5% will pay 20 or more a month. That’s a good start, but not quite viable in the long run. And getting to even those 300 will take time.
I’ve yet to see someone in the free/libre software development to make a living off Patreon.
Blender partially relies on Blender Cloud subscriptions and store sales for its income. Krita sells its version on Windows Store and Steam and also has a store for selling courses. Neither would manage to get by just off donations. And they’ve been a lot longer around, with much larger following.
Above all, this project would need a team, where different people would take care of things they are most qualified to do. I’m sure the community has people who can do marketing and training. But right now there isn’t even an active developer maintaining Natron, and without at least one developer it all falls apart. (Which is pretty much the reason I asked Alexandre and Fred about ‘low-hanging fruit’ tasks to pick for someone to start getting involved, when I interviewed them.)
Sorry, if I’m overly pessimistic.