Not very. There is a huge difference between graphics rendering and interactive UI. By the time you add proper cross platform text rendering, a proper layout system, image/video/audio (incl. multirate streaming), resolution scaling, accessibility, compositing, animation, etc. you won't have such a thin client anymore. Plus you'll probably want cross-platform consistent networking, storage and security too. Electron is so big because it reinvents every possible wheel in exactly this way to provide maximum consistency.
Plus, you will have to deal with the fact that while you can push large amounts of computation out quickly to the GPU, reading back the results to CPU involves long latencies and scheduling issues. It often results in a loss of the kind of generality people take for granted in pure CPU programming, from little things like not being able to printf() in the middle of a program, to larger things like having to manually hook up every function call in GPU land by submitting a detailed description of your specific desired calling convention in triplicate (i.e. uniforms, varyings and attributes).
The alternative model is platform specific front-ends backed by a mostly universal back-end library. Used successfully by Transmission, VLC, and others. All the conveniences of being tailored to each platform in terms of UX and integration, but with the same basic broad functionality. But few companies will want to pay for 2x the devs, while in the open source world in practice the various platforms diverge so much they almost feel like different apps entirely. Still, it is much preferable over a 300MB+ hog that can't display more than 2 screenfuls of chat.
Plus, you will have to deal with the fact that while you can push large amounts of computation out quickly to the GPU, reading back the results to CPU involves long latencies and scheduling issues. It often results in a loss of the kind of generality people take for granted in pure CPU programming, from little things like not being able to printf() in the middle of a program, to larger things like having to manually hook up every function call in GPU land by submitting a detailed description of your specific desired calling convention in triplicate (i.e. uniforms, varyings and attributes).
The alternative model is platform specific front-ends backed by a mostly universal back-end library. Used successfully by Transmission, VLC, and others. All the conveniences of being tailored to each platform in terms of UX and integration, but with the same basic broad functionality. But few companies will want to pay for 2x the devs, while in the open source world in practice the various platforms diverge so much they almost feel like different apps entirely. Still, it is much preferable over a 300MB+ hog that can't display more than 2 screenfuls of chat.