I see tablets as currently being used to CONTROL a music server, but not be the music server itself. For most of us, we will require much more storage space and more processing power for ripping CD's and distributing music data to (potentially) multiple destinations, and handling streaming audio from the Internet.
As the technology matures and the tablets get more and more powerful, then it may become possible to use the tablet itself as a music server, but I don't think we're really there yet for high-end audio data.
Michael