But I'd basically have to relinquish ownership of it? I'm not really a fan of that idea if it does. What about something like Creative Commons?
If you release your Extended World Generation Rules as Open Game Content (OGC), you retain ownership of the copyright in the work. However, you grant other people a license to use the work in accordance with the terms of the Open Game License (OGL). If create derivative works based upon your work, they must attribute your work as a source as required by Section 15 of the OGL. For example, if a publisher decides to extend your work in some way or produce UWPs based upon your methods, they must provide appropriate attribution. It is also good manners for them to communicate their intentions with you beforehand, although this is not explicitly required by the OGL.
Please note that the OGL does permit you to declare some sections of your work as Product Identity (PI), excluding it from the material licensed for reuse. The Open Game License only gives you the right to copy, modify and distribute Open Game Content, unless you have a separate license from whomever owns the Product Identity. One common approach is to release any new rules elements as OGL but to declare all proper names and other setting elements as Product Identity that is not available for reuse. Another common approach is to release 70% - 80% of the new material as OGC but retain exclusive control over the remaining 20% - 30% of the content.
Under Section 1d of the OGL, if you release a product under the license the following material becomes OGC by default:
"the game mechanic and the methods, procedures, processes and routines to the extent such content does not embody the Product Identity and is an enhancement over the prior art and any additional content clearly identified as Open Game Content by the Contributor."
Under Section 1e of the OGL, the following material is product identity by default unless you choose to release it as OGC:
"product and product line names, logos and identifying marks including trade dress; artifacts, creatures, characters, stories, storylines, plots, thematic elements, dialogue, incidents, language, artwork, symbols, designs, depictions, likenesses, formats, poses, concepts, themes and graphic, photographic and other visual or audio representations; names and descriptions of characters, spells, enchantments, personalities, teams, personas, likenesses and special abilities; places, locations, environments, creatures, equipment, magical or supernatural abilities or effects, logos, symbols, or graphic designs; and any other trademark or registered trademark clearly identified as Product identity by the owner of the Product Identity"
Speaking personally, I believe that a young system such as the Cepheus Engine can benefit from establishing a library of OGC enabling it to compete with established systems such as MgT.