Related anecdote: Screenhero's UI was originally totally native on the two platforms we supported (Mac and Windows). It was a night-and-day improvement (it looked better, had fewer bugs, was easier to build and maintain) when we moved from native UI to HTML5 (using Awesomium on Windows, and WebView on Mac). However, we'd then have issues on Mac where a user's UI would have glitches because their version of OS X or Safari (often both) weren't up-to-date. So it was always a little awkward to tell people that the reason their screen sharing app looked funny was because they needed to update their web browser.
Having said this, I think this discussion between Electron vs. Native is a false dichotomy. Performance and developer efficiency are both clearly important, and we don't have to maximize one dimension alone. I am confident we'll find a way to make Electron far more performant by switching off unnecessary features, such that it provides us just the surface area we need to be able to build great products that are indistinguishable from their native counterparts: except that they're quicker to build, easier to debug, are of higher quality (with fewer bugs), and cost less.
I know this sounds optimistic, but given the popularity of Electron, coupled with the issue of performance, this is an issue that is certainly going to improve over the coming months and years. Who knows, since ours is one of the more performance-hungry products, we may end up finding a solution that others can leverage as well.