It's only one side of the medal to work with open source software – the other side is to add creative and constructive contributions on your own. The hurdles for developers who want to actively join the Umbraco project are smaller than you might think. By following the guidelines in the quick start guide on our.umbraco.org you can easily become a core contributor yourself.
You want to contribute to the Umbraco code and add fixes and new functions all by yourself. No problem! The quick start guide on our.umbraco.org tells you how to get started in only seven steps. So get your own Github account, log on to our.umbraco.org and be as creative as you want: https://github.com/umbraco/Umbraco-CMS