I think that there is room for improvement... Flutter is something very interesting, though yet another language (Dart). React Native is also interesting, but actually creating for cross-platform has some niggles. I would think a nice cross-platform UI toolkit for Rust, once async/await drop could be huge. WebAssembly + Canvas|WebGL|SVG as a generic runtime base could go a long way to also bridging a gap.

In the end, it really just depends. Right now electron is the closest we've had to a cross-platform application base with a UI that is easily styled and a single codebase for write once, run anywhere that we've had. Most of the cross-platform UI tooling that's come before has kind of sucked. Even getting build pipelines for multiple platforms (even just Linux, Windows and Mac) has been pretty painful. Electron bridges a lot of gaps at the expense of a more bloated baseline.

I think things will get interesting and we'll see some new/old paradigms show up.