One would assume that Sony knows the UHD Bluray market better than anyone else.
The big studios have been hoping that UHD would help with the declining physical sales. This move will have them wondering what to do next.
According to Andrew House in an interview, Sony isn't seeing much demand for UHD physical media, hence the mention of only streaming UHD content.
If Sony is completely throwing in the towel on physical media, well that's a very interesting development.