MVT service of EPSG:4326 cannot be loaded on 3D map

With olcs, I can load MVT vector tile services in the EPSG:4326 coordinate system on 2D map, but after converting to 3D map, it doesn't work. 
I don't konw if this feature is not currently supported.

I have seen some related explanations [code：](https://github.com/openlayers/ol-cesium/blob/master/src/olcs/core.ts#L421-L451)
Is there any recent progress that can be revealed?
