After seeing the recent chapter I realised that Naruto got those eyes because Minato had just released that little chakra of himself inside Naruto's conscious, he sealed his little chakra in Naruto after sealing the half of Kurama chakra, Naruto got that chakra, but since it wasn't much it didn't last long and only the eyes changed. This means when Naruto gets other half of Kurama chakra Bijuu Sage Mode will be revealed.