If its going to be a Pocket PLAYER'S Guide, it only needs to have the stuff that players need. Thus, no world building, ship building etc., maybe the trade system, definitley character creation, combat, space combat, equipment etc.
Of course, it could also be the whole book if a smaller typeface is used (hopefully still a readable one) and the text packed a bit more densely.
Either way, it will be a boon to players and GMs alike.
Allen