I would say for me, the killer app would be just about anything you might reach for Electron with, but want a much smaller install footprint. Tauri in and of itself is pretty cool, kind of a lighter alternative to electron using native platform browser engine.

In general, I would probably reach for Rust if I needed to do anything wither Web-Assembly (wasm) as the path to working is much nicer than other languages imo. Along those lines, Yew is pretty nice as a rust-like framework.

I've also played with Rocket, and found it very nice and effective for api driven web-apps. Haven't done any templating engines in/with Rocket, however.