@edvin I was running ListViewTest.kt as an Application and was getting the following ClassCastException. I reworked the test case to use ItemViewModel and sent you a PR. I haven't seen your latest ListView work so it might have some boilerplate that can be removed.
java.lang.ClassCastException: tornadofx.tests.MyItemFragment cannot be cast to tornadofx.ListCellFragment
at tornadofx.SmartListCell.updateItem(ListView.kt:157)
at javafx.scene.control.ListCell.updateItem(ListCell.java:471)
at javafx.scene.control.ListCell.indexChanged(ListCell.java:330)