I am past caring if it is a totally native looking toolkit, just as long as it looks good/consistent across all platforms with hardware acceleration I am good to go.
Well, given those bullet points, Servo might meet your needs :)
In general we're not going to think about blessing packages as "official" unless it gets to the point where some package becomes mature and overwhelmingly dominant in its space (think Rack in Ruby or async in Node); we'd prefer to focus on making it easy to upload and share Rust packages via Cargo to build up an ecosystem.
With that said, the last time I heard, the reason for Rust's existence (Servo) did not have any plans for implementing anything outside of the browser rendering & javascript engine. So, no browser chrome, which would be the only reason I can think that they would develop an "official" UI toolkit.
I would love for someone involved in the project to correct me, though :)