You get a job, (or curry favor), with the people who work in eBay's Magento division. In other words, you probably don't fix the core issue as a project outsider.
Magento has always favored a centralized, close-door approach to development. They make something, release it under an open source license, listen to what people say about it, and then release something else.
There have been times during Magento's life where, if you signed a contributors agreement with Varien Inc. or Magento Inc. (the two corporate entities that were "The Magento Startup" pre-acquisition with eBay), you could submit patches for bugs and/or new features. However, that petered out (post acquisition?), and contributors were blocked from Magento's internal Bug tracker where information was spread and patches submitted.
Right now Magento's in a weird limbo state. Internally, their development team is working on Magento 2, and dropping code every so often into GitHub. They accept bugs and consider pull requests/patches there. However, the original Magento 1 CE bug tracker is off line right now. The last time Magento spoke semi-publicly about this it sounded like 1.8 would be the final Magento CE release, and new efforts would focus on Magento 2.