Variation selectors aren't respected for PUA characters. This means that characters encoded in the UCSUR, for example, sitelen pona, won't be able to make use of them to show variant characters.

STEPS TO REPRODUCE

This requires the nasin nanpa font to render the needed PUA characters. Download the version labelled UCSUR.

QML:

import QtQuick
Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")
    Text {
        font.pixelSize: 100
        font.family: "nasin-nanpa"
        // [sewi] [sewi][VS1]
        text: "\uDB86\uDD5A \uDB86\uDD5A\uFE00"
    }
}

Expected appearance (taken from Firefox):

Actual appearance: