Dev Hub for open source?

I use a Developer Edition. As you say, it is limiting: if you want to run continuous integration flows like executing Apex unit tests on every push or every branch, you're going to have a hard time of it. Ultimately, you'll either need to pool Dev Hubs or dramatically limit the scope of your testing, such as only running CI tests when a pull request is opened. I use one Developer Edition Dev Hub for local testing and a separate, dedicated one for CI.

There is an open Idea on providing Dev Hubs with higher limits for open source projects. Please give it some votes!