GOG would be in a much better position to get System Shock 2 working than someone working by themselves in their free time from a retail version of the game. For starters they may well have the source code. Which would make things substantially easier.
You seem to be forgetting that GOG have faced similar problems with a great many titles already in the catalogue. That is basically the whole point of GOG after all. They're not doing this to display the corpses of long dead games, but rather revive them.

To summarize the rumors, GOG is introducing:
Infocom, creator of the unexcelled Zork adventures (30%) - see Google
-or-
Origin, having developed a role-playing interface of unexcelled friendliness for its hugely successful Ultima series. (10%) - see Google
-or-
It could be a pun on Deus Ex (30%) - since it's about time
-or-
They are coming out of beta with XP, Vista and W7 support and will revamp the GUI and take out the BETA tag (30%) - since it's about time
Sounds pretty good...

Sure they would, but after viewing what SS2 would require for a stable and fully supported release, it's not really possible today. They would also do a great thing with releasing Ultimas, which reqiure far less effort, they run well in DosBOX.
I've always viewed GOG as a D2D distributor with use of DOSBox, SCUMMVM and such, and not a source-code reprogramming company. So, has GOG ever REWRITTEN a game? I'm new here, so i'm don't have all the facts here, i'm just asking.;)
I just don't really see GOG doing something that surpasses [excells;P] Kolya's effort.
Well, i don't know many of the GOG titles, mainly because i had no interest in them when they came out [like MYST, i know, blasphemy for some;P]. I specialize in the late 80s early 90s games mostly, didn't care much for games after 1997/8 with some notable exceptions like SS2. I'm a necrogamer, i do fine with corpses, i still play my C64, and spit on Crysis.;P I think i know what GOG tries to/does accomplish.
If i don't see something, or i'm wrong, i'd be happy to be corrected. ;)

Well, I played the demo and liked it. I just couldn't find it anywhere.

GOG have a full time team of professional developers. Kolya is one person who has dedicated some of their free time to the effort and only has the retail version of the game to work with. Having the source code makes all the difference.
A couple of examples:
Earth 2160 - If you're at all familiar with the game before it came to GOG you'd know it was notorious for being unplayable on almost every system. GOG did a great deal of work to get it fixed up.
Sanitarium - The retail version I first played was busted up far worse than how you've described SS2. So much so that I had to give up on it in the end as there was no speech or video and the text was only there for a brief instant. The GOG version works perfectly on all counts.
There are no doubt many more that required a great deal of work. But I can't personally tell you how much of a difference GOG have made to them.

I am pretty sure the announcement is that EA is coming aboard the gog.com train of awesome and they are releasing Sistem Shock 2 (or 1) on tuesday, blue background with stars anyone? so obvious...please be true :(

If it still exists, why wouldn't they be? For GOG to sell the games here would require EA's cooperation. If EA aren't up for cooperating then we'll know that because their games will continue to be absent from GOG. Of course, it wouldn't be the first time that the source code was lost.
I'd imagine that it was mostly through stripping out the DRM, as it was that which caused most of the problems. They don't tell us specifically what they've done to make the titles work. It's just sometimes rather more obvious than others. Including the two examples given.
Mods often continue to work with games. Even when the game is running on a completely different OS than was previously supported by the game. But yes, some mods might cease to function/be made obsolete. Especially those you describe used to get the retail version running. But mods that offer improved models and the like should still work.

A lot of the games on GoG are fairly poor by today's standards and strictly for those who played them the first time round so a game that's unsurpassed is something unusual. I guess it'll either be a game who's strength lies in an Area that hasn't improved much (Baldur's Gate 2) or is part of a genre that's out of fashion at the moment (Sim City 4, Independence War 2).
I wonder if the background image is significant. The glow stops behind the numbers so I wonder if they could be hiding something that's blocking the light? Four people? Four vehicles? Four letters?

Well, let's remember it's EA we're talking about here, so my bet would go for a limited distribution license. Sourcecode would be great, but i've noticed companies tend to value that more than anything [Atari still withholds Blood's source].
Too bad source code does not end up in the extras, as it would give new life to some games. Jagged Alliance 2 was released with it's sourcecode on the Gold edition. And the v1.13 mod which was based on it, made me play that game again, and i'm still playing it today, sometimes with friends, thanks to the added multiplayer.
On the other hand, some great GOG games, like Duke Nukem, whose source came out, could use a revamped multiplayer. If GOG is giving new life to the games, why not resurrect it's MP?:)
Oh, i see, I didn't thing about the copy protection before. When i first heard of GOG being DRM free, i thought that they've contacted the respective authors of games for a "clean" exe and such. Though Your assumption is valid, I wonder if GOG strips the games by themselves.
Well, mostly so, unless the changes in the code render the mods incompatible, i think GOG had this problem somewhere before, not sure if it wasn't JA2, but i'd have to research that.
As of the completely different OS's, Well, *nix/mac support is yet to come. GOG still is Windows only, and even though every edition has a lot of chances, usually some standards remain, like DirectX, which is backwards compatible, and most games that use DX in the correct way, will have no problem running on modern ones.
For example, if the only thing that needs to be dome is stripping DRMs from a game, that would not really make mods unplayable, but if the game by itself is incompatible with modern systems, because it relies on more or less ancient designs, or long forgotten functions [System Shock 2, Dungeon Keeper] then the changes to the code may inflict mods unplayable. I was thinking about gameplay enhancing mods, upgraded/tweaked AI, fixed bugs that were not done right in the last official patch, etc.
Hm, maybe it was the GOGs Fallouts that didn't like the unofficial patches? I should have payed more attention to that thread some years ago..
Anyhow, all we can do is wait and see, and perhaps not get overexcited with the "Expect" part, and think more of the "Unexcelled", then we shouldn't be disappointed in any way.;)

Man, that's harsh :\. Also - what are "today's standards" ? Only the games that relied heavily on their looks would age fast. The only other thing that might be easily improved upon nowadays is the interface, because limited resolution forces limited UI features (and limited world view).
Everything else - the music, sound effects, plot, feel, gameplay - is not that simple (though - not impossible) to improve upon.

Not behind door number one ! . . . =)

I find your lack of faith disturbing.

I had that same problem, played the demo and loved it but couldn't find the game in shops so I grabbed it off ebay second hand for £1.

I just noticed it, I'm just dying about this unexcelled thing.
What's that you've come up to after 15 pages of discussion, guys :-O