Alright please excuse the self-promotion, but I've been working on azul for a while now. It was supposed to be the successor to limn - I talked to the author of limn and limn simply has the problem of verbosity - while it's possible to develop GUIs in it, it's buggy as hell and not really easy or straightforward to do. limn has serious state management problems.
For some reason, people thought that azul was already finished, hence the big warning in the header. But for anyone needing ideas on how to practically implement a GUI toolkit without inheritance in a MVVM style, read through the README.
Servo won't become embeddable, that's something I can say with confidence. I tried. Servo is even more bloated than electron, the JS parts are heavily tied in with the rest. A servo app takes 70MB of disk space (stripped) and 300MB RAM - which is fine for a browser, but not for a desktop app. azul, which just uses webrender (the rendering engine from servo), uses only 5MB binary size and 39MB RAM - quite a difference. azul has its own CSS engine, because crates like html5ever and stylo are heavily tied to the Firefox architecture, which is simply way too complex and doesn't fit my design goals.
There are things that aren't finished yet, notably the layout and compositing system. I use this at work to create a desktop application, so.. yeah, I'll just continue developing it and tell people when I'm done with a 0.1 release. But I haven't hit large roadblocks yet... I just need time.
I already have a half-working GUI system in my production app, however that app is proprietary - I'm trying to "outsource" as many components to azul as I can, in order to keep the app lightweight (currently 10k lines and that's already too much for me). The more I can put in azul and forget about, the better. In order to use it at work however, at least the layout system + the SVG system should work, so that's what I'll mostly focusing on. I'll probably finish a 0.1 release this summer.
Sorry if this is against the rules, but I just saw this thread pop up and wanted to tell people - things are in progress.