1) It can have new features - the are some upstreamed from KDE, and it's just about users coming with new proposals - nobody cames, no new features. Easy.
2) Why would you change something that needs no changing?
3) Lot of efort goes to QML, yes. Why not?
4) Maybe. Nothing prevents you from writing QWidget equivalent of the "cool" QML widget and upstreaming it.
Obsolete stuff is unmaintained. You can rest assured that QWidgets will be maintained and bugs will be fixed.
Obsolete stuff is unmaintained. You can rest assured that QWidgets will be maintained and bugs will be fixed.