Qt license is USD 5500 per user per year. For Sketch developer, this should not be an issue. But for some developers who bootstrap the cross-platform application, this might be an issue.
Also, C++ programmer is more expensive.
The cheaper option would be JavaFX. IntelliJ IDEA is one of good cross-platform application examples.
Thanks, I don't agree with the "good" part of intellij idea. Popular, sure. But slow as hell and ram hungry.