Currently the digital teleconverter is only available in jpeg only modes.
According to the documentation of the Leica Q, the 'trim' feature (that's how they call it) of 35 mm and 50 mm is available in all image modes. The DNG (raw) however contains always the full 28 mm view + data indicating the trim value.
It would be nice if Fuji would adopt a similar approach (to be included in a future firmware upgrade) and allow the teleconverter to be used in jpeg+Raf modes.