I still think you need some sample aliens in SMU core, if only to show what the system can do. You cannot avoid some setting information, because there will be some base assumptions about future technology, for example. That's far more structural than the races in the core book, just as replacing Spell Law is a lot harder than just replacing RMU races with new ones. For that matter, even sticking to humans, you have to expect variants in interstellar civilizations, whether purely due to random genetic drift, evolutionary pressures in new environments, genetic engineering, or various mixes of all three. You could easily have over a dozen listings just for human types. But if the core doesn't address aliens, that's a pretty big hole to leave in a generic system. "Humans only" is an assumption for specific setting.
That said, I don't think there needs to be a setting in the core book, anymore than there is for the fantasy core. You should be able to play a version of the Traveller Imperium, the Star Wars galaxy, the Firefly 'Verse, or the Star Trek future with SMU. Some of the tech specifics might need more specialized books to flesh out (power swords don't belong in core, but in a weapons expansion; there are so many variant FTL drives, not to mention STL drives, that only a few can be touched on in core and even those should get further fleshed out with possible variation in a starship book), but the base should be flexible and expandable to support many different futures.
