> You can't push to origin unless it's your own project or your team's. We're talking about PR-based workflows.

Having to create a fork per PR is a rather antiquated way of doing it. In my experience, you can almost always push to origin and create a new PR from the branch, but maybe I've just been lucky with the projects I contribute to.

> It's not a constant cost, unless you're saying you only ever intend to contribute to one project ever. It's a fixed cost that you will pay N times, where N is the number of projects you contribute to.

It's a constant cost in the same way that looking up where to submit your patch to is a constant cost. You will pay both N times, where N is the number of projects you contribute to.