I'll give my final thought to this (until I hear from Panny)...
Skype will definitely not make it to my VieraCast. My TV has no USB port, hence no mic/camera availability.
However, I see no reason why the rest can't be on there. Netflix is technically equivalent to Amazon VOD, Pandora is just streaming (like YouTube), and Twitter shouldn't be a problem either, since it is 140 characters, I don't need a keyboard for that.
The Fox Sports is another concern tho in that interactively overlaying stuff over an image may require different hardware.
So, that's my $.02.