Scifi is a rather broad term. It's not likely to be hard scifi, but more likely either near-future or some kind of Firefly style future that is both approachable, yet also retaining scifi elements.
With the direction and development of new Blizzard tech in recent years, I also believe it will be casual-friendly like WoW (whether that is a good or bad thing) and rely heavily on the phasing/cross-realm zone style technology they've been developing. It's likely to be either very few servers, or only one universe. My question is how they would handle the character namespace -- would character names be non-unique then and messaging would just rely on your unique Battle.ID I guess?
I just hope it has a lot of sandbox elements to it and a full-fledged crafting system ala Starwars Galaxies. I'm afraid the slippery slope of WoW going more and more towards broad, homogenized, casualization will make the game bland and not have staying power for me. I'm not really in the mood for hardcore raiding anymore, but I still feel like handing out lots of items for little to no effort is bad game design even if it makes people feel better.