So... can you take weapon focus in starship weapons?
If so, would that be a class in itself, or would you need to break it down? Is so, how?
Both? e.g. Light tracking weapons
From a balance point of view, starship combat seems to be in about 1/2 the scenarios and a maximum of one encounter, so having just weapon focus (starship weapons) would seem probably okay.
Looking at how the other weapons are arranged, each type has a table to it. (basic melee is table 7.1) I note all the starship weapons appear in the one table (9.2 Starship Weapons) - which would seem to agree with that as well.
As this is the rules forum. Since there is no way to get weapon proficiency with starship weapons you don't have the prerequisite to take weapon focus with it.
As a GM if you want to sell me on spending a feat for +1 on starship weapons I'd be fine. But its not in the current rules and I wouldn't expect it to appear anytime soon.