Yeah they're going to work on 3D afterwards (potentially, the main dev for 3D left the Flutter team and is back on Android if I recall correctly), it's not a huge priority right now. Also, it's not recommended to use GetX, there are some issues with it, a major one being it's like a framework within a framework, and it essentially rewrites a lot of Flutter. Better to use Riverpod, Bloc, Signals, ReArch or something else.
For 3D however, I've been looking at Dioxus which is in Rust, they're making a native renderer the same as Flutter (ie not webviews) called Blitz, and they're making good progress on the mobile side. This renderer can embed Bevy, a game engine also written in Rust, and Bevy can also embed Dioxus native, which I thought was really cool, it's bidirectional embedding.
I didn't know Expo explicitly made you pay, I thought it was only optional. Now that I look at it, seems like it's for high priority builds but still, can't we just build on our own servers? If not then that's a big con, I don't want to rely on an external service just to build my app.
What are you making in Flutter?