I'm just blathering. SWTOR is currently a ghost town as it is, but if you were to play it offline, you'd never see anyone out in the world, you'd just have your static NPCs. To properly make a SP game out of it, you'd at least want to put roaming groups of friendly and hostile NPCs...? At least to simulate some small part of the worlds being 'alive'.
This might be my singleplayer bias coming through, but... why would seeing random players running around be considered essential? Or even a good thing?