This may not be the message of the article but as a side-rant: I really don't understand the use-case for a Rust-based GUI. Rust's syntax, manual memory management, and compile times makes it seem like it's really not meant for this kind of workload, but instead for things like compilers, embedded systems, that kind of thing. I understand that not every UI needs to be a cross-platform blah blah blah written in TypeJa…
I looked into Rust for writing games (including the UI frameworks), but found that the power it provides isn't really worth all the mental overhead. Most games don't really need that much power, particularly if you are using non-realistic graphics. In the event that you do actually need extra optimization, most engines let you hook down into C++ for raw performance.