We might switch to Tauri someday. Death-by-a-thousand-cuts is a very serious risk for us though, so we're trying to choose the most mature and widely-used tools whenever possible.
As noted on our website, we still have a lot of work to do on security (including some open issues you could probably tackle! and thanks for expressing interest!!) so it will be a wonderful day when Electron's lag in staying up to date with Chrome security fixes is our most pressing security issue!
In the meantime, if Signal chooses Electron that is a good indicator that, all things considered, it is a good choice for us. They have a lot more resources than us, are much farther along than we are, and they take security seriously.
One immediate issue with Tauri, just to give an example, is that it would require us to worry about Safari quirks on Mac.
I've also heard from projects in our space that the handling of platform-specific functionality outside the browser window is not as mature in Tauri as it is in Electron. This is totally understandable and Tauri is a great project with great goals, but the possibility of running into some deal-breaker Windows-specific issue, say, is scary.