For those with the book..

What are the skills like?

Do they have depth or are they overly simplified?

By "overly simplified" I mean, does one skill check cover three or more wholly unrelated tasks and ignore the complexity and radically divergent nature of skill and knowledge required for certain tasks to be performed for the sake of simplicity?

or

Can the janitor fix the toilet and the starships drive core with the same skill?

As to character classes…

Are the gun bunny types tough and stupid or can they actually function within society by not shooting people?

Who knows how well the space-janitor does with the hyperdrive, but I think the whole point of this game is going to be that even the bounty hunter owes child support to somebody back in the Core, a noblewoman with a really good Imperial lawyer. Most of my assumptions are based on what I know about Warhammer Fantasy, and I wager that no career will rely too heavily on the combat element of the game.

Also, the GM can always add the equivalents of misfortune and challenge dice to any roll for any reason he sees fit. A janitor who's feeling lucky can see how well the hyperdrive responds to his own common sense, with a couple of extra challenge dice thrown in, which will bring a greater chance of blowing up the ship…

If it is like WFRP 3rd, expect very general skills. It is not a system that deals with specifics in great detail, especially as you have to make all skills roughly equally valuable. No one would ever take "Space Toilet Repair". Also, broad competence fits the genre better than narrow specialisms. You might find a hero who is a good engineer. The fact that he should really be specialised in one area (say hyperdrives) doesn't usually stop him fixing space toilets in this kind of thing.

If necessary for a Space Janitor (is it even a character option?), you could create an advanced career skill called "Space Janitor". This would be rolled for every task that could conceivably be covered by being a Space Janitor, including minor repairs, leaning on mops and shouting at annoying kids who mess up the paintwork on the space bike shed. This would mean they would not have the general "Repair" skill that lets them rebuild hyperspace engines from scratch.

On characters working outside their niche: If it is like WFRP 3rd, which the more I heard about it the more I am sure about it (though with many many tweaks), then as long as players don't min-max out of the wazoo they will be able to do general tasks outside their niche. However, in WFRP 3rd specialists have yellow dice (or expertise dice), which tend to unlock certain things (due to a special symbol only on that dice) and are the flat out best positive dice in the game, so tend to get better results (or are more reliably able to do more difficult tasks). However, if they totally min-max (Strength and Toughness 5 Trollslayers, I am looking at you!), then they will just fail at anything outside their niche. However, personally I feel the WFRP 3rd system is one that generally encourages more balanced characters anyway.