Wow. That's tough. If a working demo doesn't convince them, I'm not sure what will. "See this? Do you want this?" is a pretty simple question. Do they need more evidence of unit- and integration testing? Do they need some/more user feedback before proceeding?

Remember, some people don't listen to reason, some of your wise seed will fall on rocky ground, and don't try to teach a pig to sing. I'll stop now :-) Best of luck again.

It's mostly code quality / style / archtectural objections. Some of which are understandable since I'm new to the codebase and it's a prototype to show the feature, but taken together all the feedback basically rewrote the entire feature. I've pretty consistently had better experiences contributing to large open source codebases than getting a feature into this codebase so I don't necessarily think it's that I'm bad at receiving feedback?

They might be seeing you as a threat, because they think you might be trying to steal their light.

I used to not want to believe this kind of thing, but when I started to believe in it, quite a few situations became simple to understand.