Dynamic show/hide of model parts in Hololens

I think this should be doable. You can start with some basic code to highlight a part when you tap on it:

// this handles user tap on an item
$scope.PART_HIGHLIGHT_COLOR = "rgba(255,0,0,1)";

$scope.$on('userpick', function (event, targetName, targetType, eventData) {
 // variable to pull the value for the occurrence property in the eventData JSON object from the model. Create variable for the currently selected part
 var pathId = JSON.parse(eventData).occurrence;
 // turn off previous highlight
 if ($scope.currentSelection) { 
 tml3dRenderer.setColor($scope.currentSelection, null);
 }
 // get new part and highligh
 $scope.currentSelection = targetName + "-" + pathId;
 tml3dRenderer.setColor($scope.currentSelection, $scope.PART_HIGHLIGHT_COLOR);
})

 Then you can add a button that selects the parent of the current selection, which would basically involve stripping the last "/##" from the end of the occurrence, something like this:

$scope.selectParent = function() {
 if ($scope.currentSelection.includes("/")) {
 // turn off previous highlight
 tml3dRenderer.setColor($scope.currentSelection, null);
 // strip off last entry in occurrence path
 $scope.currentSelection = $scope.currentSelection.replace(/(.*)\/\d+$/, "$1");
 // highlight new selection
 tml3dRenderer.setColor($scope.currentSelection, $scope.PART_HIGHLIGHT_COLOR);
 }
}

As for how to hide items without explicitly defined modelItems, I think there's probably a way to do so via tml3dRenderer, but I'm not sure exactly what it is. You might be able to work it out poking around in the VS javascript code or poking at the tml3dRenderer object in the browser debugger tools.