WoW speed won't ever be possible I believe. First of all WoW is pretty much the fastest (3D) MMO to boot.
The real reason though Home can never boot up that quickly is because each time you do so the service finds a new server/dimension for you. As a MMO gamer you are locked to a specific persistent server forever (disregarding paid transfers), it always know where to go.
The number of servers/dimensions in Home is dynamic according to number of players online. Also, Home will have to 'matchmake' you into an appropriate server according to inhabitant numbers.
With that said though, I see no reason they couldn't shorten the boot up time to a third of the current one. It's just badly designed atm. Boot directly into the world. Have the daily message in game. Also, have a confirmation (Yes/No) in the XMB when clicking the Home icon.