do you have a problem getting to all your youtube subscriptions through the bravia internet tv - youtube application (excluding VEVO channels)...? Most of my subscriptions have disappeared since I have updated my software.
There is a bit in the Smart TV FAQ on Youtube. But it likely comes down to the rights that Youtube have, i.e. they don't have the rights for the big screen device. This would be the same for all smart TV's from all manufactuers, so its likely that any premium content is locked out from Youtube at the moment.
This may well change in future however, but this is out of Sonys hands and squarely with youtube.