Electron might not be "fast" enough for many serious GUI applications? That been said, I also am struggling with finding a non-Java cross-platform GUI dev platform. The selection pool boils down to between QT and Electron indeed these days.
Personally, I'm keeping my eye open on libui (https://github.com/andlabs/libui/) as it is already possible to do some basic things with it. However, it is pretty much in alpha state and I'm slowly writing the Python bindings for it at https://github.com/joaoventura/pylibui/. The thing that I like in the libui is that it is a thin wrapper around platform specific frameworks. Therefore, the library is very small (some 340 KB) and it's as native as the underlying platform calls are..
Regarding Electron, I am writing an application on it, but it is too god damn heavy in terms of memory, disk space and boot time, and web front-end development is absolute chaos these days. Although I'm currently writing my app on it, it is mostly an MVP as I want to make pylibui/libui usable enough to switch to a pure desktop cross-platform library asap..
Try Sciter HTML/CSS engine then (http://sciter.com). It is a monolitic DLL (4-8 Mb) without external dependencies. Works on Win/Lin/OSX and even on Raspberry Pi 2 - http://sciter.com/sciter-on-raspberry-pi-2/
However it lacks in some areas, such as the scrolling which is quite bad, and it does not render the SVG files that I'd need it to render (tiny SVG spec, but lots of defs and rotations). I'm still going to look better into it since I can use Cairo and CairoSVG to convert my SVGs to PNGs, but I still do not know how well it renders some css rules, fonts, etc..