Maybe, but I got the sense from the article that what NVIDIA has patented are the semantics of the API itself (i.e. the types of messages sent between the CPU and GPU.) A polyfill for the API might still be infringing, given that it would need to expose the same datatypes on the CPU side.
And even if it wasn’t, the path-shader semantics are so different from those of regular 2D UI frameworks, that a 2D UI framework implemented to use path-shading, that falls back to using the polyfill, might be much worse performing than one implemented using regular CPU-side 2D plotting. It would very likely also suffer from issues like flicker, judder, etc, which are much worse/more noticable than just “increased CPU usage”.
And even if it wasn’t, the path-shader semantics are so different from those of regular 2D UI frameworks, that a 2D UI framework implemented to use path-shading, that falls back to using the polyfill, might be much worse performing than one implemented using regular CPU-side 2D plotting. It would very likely also suffer from issues like flicker, judder, etc, which are much worse/more noticable than just “increased CPU usage”.