A space sim, first and foremost.
While some things could be made RPG-like, independently tracked reputations with various groups, selectable species and character look, possibly background as well, choices and consequences or stats for crew mates (I envision three stats: pilot - how well does crew member pilot the craft, while you're, for example, busy picking base defences off with turret; gunner - the other way around; tech - ability to increase time ship can do without service and ability to fix damaged systems without landing, or at least without landing in a spaceport), I just don't see any way to do RPG part in a spacesim/RPG hybrid, without severely crippling the simulation part.
Allow me to elucidate:
In a spacesim player directly controls their ship, so there is simply no way character's skill could affect manoeuvring part without feeling forced, as ship's stats are fixed. Similarily, ship is not a gun your character needs to hold or sword he needs to swing - it always hits where the guns are pointing and does the damage dictated by the energy expended in a shot.
What I say, as an RPG fan (and I mean true cRPGs here, no diluted uh... fertilizer that passes for RPGs these days - see Oblivion), is that there is no way to do this well, so it'd better not be done at all.
As for FPS elements - I, as everyone else would like to be able to run around outside the ship with gun in hand, however, Braben has limited resources at hand, so this would probably mean lot of work at the expense of proper, Frontier-like spacesim part. Do we still want it?