I just wish it was more cross platform (I know it technically works on Linux and windows…but it’s not a great experience) and that it didn’t have so much churn (though they’ve stopped futzing with the core components as much with Swift 4+).
I also wish it was faster. I did an Advent of Code against some friends. I picked Rust, they picked Swift. The rust code was running circles around their Swift ones even when we tried to keep implementations the same.
Anyway, that’s a rant, but I think to your point, I feel like Swift could have been as big as Rust..or bigger given the easier use, with many of the same guarantees. I just wish the early years were more measured.