I think Swing is a non-goal of this project. It provides good interop with the DOM and core JS methods, and it makes it easy to create your own interop for JS apis that aren't in the core.
A little over 10 years ago, I ran across TeaVM for the first time (probably) on GitHub. We had been looking for a way to port Codename One to the web, but we needed thread support, which wasn't supported by any existing solutions.
I emailed Alexey (the creator of TeaVM) to ask if he had plans for thread support, and he replied that, while "proper" threads weren't possible, he had some ideas for supporting green threads. Over the following 6 months or so, Alexey would share updates on progress he had made on the thread front. In March 2015, he shared that he had found a new approach for async code that wouldn't affect the performance of single-threaded code, and would support natural stack traces.
We released a preview of our web port using TeaVM a month later, and it exceeded all of our expectations, both in how easy it ended up being to do the port (because of TeaVM), and on the performance.
Alexey's solution for supporting threads, was truly a piece of genius. Had he not created TeaVM, and added threading support, I don't think we would have ended up with our web port - or, at the very least it wouldn't have ended up performing nearly as well.
Nice. I haven't used Flavour for anything yet, but TeaVm is awesome sauce! This past year or so, I've noticed an uptick in activity surrounding TeaVM. More contributions from people other than Alexey. Some of this is seems to be related to the growing interest in WASM solutions, and TeaVM is probably the best pathway from Java to WASM right now.