More suns = more than one main light source = EXTREMELY difficult. Actually, the engine can't really do it. I'd have to rewrite it.
Note: the stars are already unique per world... but there is only one sun and one moon and I have no plans to change that (see above).
Oh, no, I meant like adjacent to eachother. If suns and moons were just haphazardly placed about, that'd be a mess. Consider it more like the possibility of the sun or moon having an additional star or moon like satellite.
Things like these twin stars(which are actually quite common in solar systems):
Coupled with recoloring of astral bodies, you can make a truly alien planet that has a completely different atmosphere from what we think is a normal environment.