If by "revallistic" you mean "relativistic" then it doesn't make much sence as speeds in Orbiter (up to order of tens of kilometers per second) are far cry for any relativistic effect to manifest itself in any noticeable way...
I'm sorry if I misunderstood you.

asmi is right.
You would have to gain about 100 000 - 200 000 km/s to see a little diffrence, which is not possible w/ any realistic or unrealistic add-on in orbiter.

It is certainly possible with unrealistic add-ons, most of the star trek ships can be run up to significant fractions of c, as far as I know.

It's also possible for realistic add-ons, if you take a generous measure for realistic (also, I can reach significant fractions of c with almost any ship, just give me high time acceleration and a lanet to bump into ).

Martin once mentioned that he thought about going relativistic, as he would consider it an interesting challenge, but that certainly wouldn't happen anytime soon...

I think speeds upto c ....in fact far beyond can be reached in orbiter easily simply because its representable by double precision. But the movement of the vessel will have to be controlled by the plugin with the effects provided by a graphics client.

see...its all easy

Everything sounds easy when it's not you who will have to implement that

I didn't quite get what double precision has to do with the issue. It's technically doable, but here is the thing - even coarse calculations (ignoring relativistic effects) shows that accelerating from zero to c even with 4G acceleration (limit for average human) will take 300 000 000 / (4 * 10) = 7500000 seconds = 2083.3 hrs = 86.51 days, or almost three months, during that the vessel will travel (a * t^2) / 2 = 1125000000000000 meters, or 7500 AUs, which is FAR beyond the border of the solar system

Yes. Martin does right by not working on it, because there are many more important things. I think most of orbinauts won't ever notice time dilation in Orbiter if it would be implemented. Why? There's a proof:
time travel

I can't see a way to do time dilation via a module. I'd say its impossible without a severe change in the core architecture, as currently orbiter simply doesn't support more than one frame of referece, and all calculations are depending on the global time.

I meant if I deliberately set the vessel's speed to 100c it will probably still get accepted accurately. Yes I know it takes a long time with current systems etc etc .

Yeah yeah I am not asking you or anybody else to do it . Simply saying that the numbers are small enough to actually fly a ship at multiples of c in Orbiter. Accurately simulating its consequences is tough of course.

Well one can take control of the ship's position(resetting it every frame) and maintain one's own clock in the module.

Position alone doesn't do the trick. You have gravity to concern yourself with, which will be a lot harder to manipulate.