All we would really need is the ability to link to a GitHub repository. This is what one looks like:
Someone with write permission to the GitHub repository could click “merge” and the changes would be integrated. GitHub has cool stuff like bug reporting/feature requests, reviewing changes to discuss, and automatically running certain tests and preventing merge if they don’t pass (like checking if the file is a valid format for memrise.
Here’s an example of a pull request in the OpenSSL project, it’s a technology that powers a third of all websites on the internet (and probably GitHub itself too!). There you can see an unaffiliated volunteer donating his time to improve OpenSSL. The volunteer is treated just like someone employed at the OpenSSL foundation. It’s beautiful, really.
There’s an off chance I might write a service that does this- but don’t count on it.