I don't know about a dedicated Space theme however so long as LEGO does release an original line every couple of years then I will be content. While Star Wars is generally good and I can recall my initial excitement when the collaboration started back in 1999, sixteen years is enough to fatigue anyone even if they are a big fan of the films which are good, just not the only saga through space out there.
Anyway my desires for an 'in-house' Space theme by LEGO aside from some fresh originality would be to see the many good translucent colors from the older astronaut teams return such as trans-green or trans-blue for example in the windscreens, antennas, etcetera. Lately almost all options have been restricted to trans-clear, trans-brown, and trans-black on windscreens which is alright in some cases especially realism yet those hues do not standout compared to the more vibrant tones used in years past. The likes of Futuron, Spyrius, or Ice Planet made a mark for their signature color schemes.
I can understand LEGO's reasoning behind designing the sets to have clear-cut "good & bad" sides duking each other out as it was with Space Police III or Alien Conquest. However going back to basics of exploring the universe could be a good thing. Even better if they included otherworldly life forms as friendlies instead of the clichéd enemies bent on fighting, destruction, galactic conquest, or whatever it is this time. As mentioned, perhaps they could do something along the line of life in outer space. If LEGO is rather set in requiring an opposing faction then how about a group of space miners searching for rare ores across different worlds which inevitably leads to encounters with the local wildlife?
Although I don't mind a few Space characters sporting the aviator type headgear, the regular biker's helmet or even the newer style helmet (Series 1 Spaceman) is preferred. Galaxy Patrol's spacemarine helmet is real cool but no visor option. Whatever the helmet, air tanks are a necessary accessory or at least I would like to be given the option to have one or not.