I am a bit confused by their moving from C++ to Swift instead of Rust. It sounds a bit Apple-first. I get that it ports to Linux okay, but will it be hard to make it work with Windows some day?
The main reasons were that Swift supports OOP and Rust doesn't (useful because web standards are object-oriented and it's easier to follow the specs when you can model them in your code), and that Swift supports C++ interoperability instead of just C interoperability like Rust (makes it easier to incrementally move to Swift in an existing C++ codebase).
Rust makes more sense if you were to start from scratch, but the Ladybird devs said that their code is already heavily OOP, so it maps to Swift a lot better.
Also, variety is good, we have Servo in Rust (although I wish they'd make an actual browser around it too).