tried searching? There won't be a separation between client and server but every XBMC instance can act as both. So you can use XBMC as mesh OR make one instance act as "server". And AFAIK there will also be a headless mode (= no GUI required) so that it could also run on a NAS i.e. Will take some time until this is ready though and there might be some conceptual changes along the road - but that's at least the current vision which is being worked on.