I'm not good with mechanics, but I could give you some character and/or story ideas. The player could be a cyborg (Terminator kind of cyborg) with a human coating that acts as the security for that ship you mentioned, but the accident that leaves almost all of them dead frees you from the central computer and you begin to think on your own. In fact, having several choices for characters, each with their own starting points, attributes, and path through the story would be pretty cool. Some of the characters would meet each other if you didn't choose them, and some would never see them, but could hear about them.

I don't have much, but I've always thought a few ideas would be pretty cool if put into a text adventure mold. For example, a good/evil mold that isn't you being either some demon who eats babies for breakfast or some saint who brought light and happiness to a million children. Some shades-of-gray choices that don't have immediate consequences that you can see (The Witcher is a fine example of this) would be interesting, like finding a man in a prison who says he's innocent. What would make it even more fascinating is if your choice had consequences that were randomized. Say you let the man out one game, he joins your party and helps you on your quest. However, when you do the same action the second time around, he uses the opportunity to jump you, takes a bunch of your inventory, and runs off cackling. Death would not be a good thing to randomize in a situation as this, because it just wouldn't be fair to the player.
Another advantage with making an entirely text-based game in this day and age is how big you could make the ship. Making a ship as big as ones on Star Trek and Star Wars is possible. The size probably wouldn't even be a big issue when it comes to making a portable version, since a large text adventure like Zork takes up very little space on most modern phones. You wouldn't even have to worry about making the game work on other platforms; as long as people enjoy it, they're more than willing to mold it so that it will play on their iPhones.
Probably the biggest problem with some of my ideas is that they may require too much work. For example, that scenario I just explained must be hell to actually code. But with the absence of graphics, some ideas may be more possible for a small team to do than it usually would. Also, since many of the users here have more than one language they know, translation seems like it could be easy to pull off. I never really thought about this until now, but it seems like a perfect time to bring back low-budget text adventures.

The basic concept sounds an awful lot like Red Dwarf :-D

There are differences... Like ship drifting in the middle of nowhere because of not-working AI instead of idiotic AI :D

With space settings have you considered how to handle gravity? In most cases (for the sake of convenience) it's set to Earth's ~9.8. Fewer uses near zero (obviously there is mass) or a weak effect from the station's rotation.
But the lack of it changes many things; the effects of momentum are more obvious, bone and muscle degradation occurs, the ship design allows interactive objects to be placed on any surface not just the 'walls' and so on.
If sections of the ship, or groups of survivors have developed in a different gravity environment from others, will their interaction with others have any effect?

I was thinking more along the lines of System Shock,but that's probably because of the avatar + nearly abandoned space ship.

If you know C++, why not just code it in that? Going from my own programming experience, you shoud be able to build a program backbone that contains all the rules of the engine (once you've settled on them) and has hooks to individually call external scripts that actually run the story.
That way you can keep the design modular and make modding simple as hell. Make a quest template that you can just fill out that keeps most of its data internal but can pass flag information to the main program (eg: Quest_Complete_SHODAN'S_PUPPY = 1, Add_To_Inventory = "Super Kill Deatrh Cannon +1")

I know, that is precisely what I want to do :-) But I have to remember all the forgotten knowledge about C++ first :D

Ahh if I can learn & re-learn programming then practically anyone can. Don't know much about C++ but I could probably build something like this in a HTA with attached VBA scripts with the added bonus of being able to add limited graphics so if someone makes a really good role they can see boobies as a reward. Proper ones rather than ascii art ones

If I was to make an RPG system, I'd do it simple or else it'd never see the light of day. Examples of simpleness:
- Simple 1-to-5 or 1-to-10 basic attributes
- Simple 1-to-5 skill levels
- Simple rolls such as "roll Attribute+Skill or less to do that"
- Simple powers and boosts (yielding bonuses similar to that of skill levels)
- No classes
- No levels
- XP buys attributes/skills
- Perhaps a traits system where I could purchase advantages like "gunslinger" or "kama sutra master", or perhaps I'd save this for the advanced ruleset (Simple System 2.0)
- I think I'd call it Simple. It'd be a fitting name in a world where systems like "Special" and "Dungeons & Dragons" exist.

Amen.
RPGs have very, very complex things going on under the hood. If you're coming up with your own system you need to either a) keep it simple b) work with/hire a statistician if you're not one

Indeed. I wholly agree with that. Keep it simple. It's the story, environment and interesting game play that matters the most, not making a complex skill system.

sounds like a cool concept... were you thinking of a turn based combat system or a time based (as in actions take a certain amount of time to complete)?

I was thinking of 'normal' Fallout skill system, basically, with calculation as simple as possible. But it'll be a lot easier than 'normal' system, since I want to throw balance out of the window on purpose. But yes, if my system proves overly-complicated, I'll just make it way more simple (... I'll just throw sub-skills and sub-stats out of the window :D)
However I have never even thought of making about 5 skill levels for every skill... It would actually make everything way easier, and would be easy to make as well. And it would not affect gameplay in any negative way.
Action point turn-based system.