This sounds interesting. If the restrictions undermine its acceptance and usability.
Trademarks are a legally sanctioned, generally accepted mechanism for clarifying the namespace.
I'm not aware of any API-like copyrights having been successfully defended. Adobe claimed a copyright on the list of Postscript functions, but then immediately granted a license to re-use that list, so they've never had to sustain their claim in court. OTOH, I believe there are lots of trademark cases, partly because trademark law requires vigilance, and partly because the namespace is much smaller and therefore more contentious than the infinite range of expressions that copyright covers.