but.it's already have a Vista compatible retail version

At $10? No. Especially not with the questionable legality of the re-issued boxed copies.

Once again, the thing they are teasing can't be just a single game; the big announcement has to be a new publisher coming to GOG. Each of the clues refers to something related to that publisher, either a game they have published or perhaps a developer they have worked with. You are thinking on too small a scale by focusing all the clues on a single game. Considering P:T was published by Interplay and Interplay is already on GOG, that can't be it.

"Deus ex machina" is a plot device used in fiction by which some problem or plot point is unexpectedly, and arguably unfairly from the point of view of the audience/reader, solved or brought to a state of closure. For instance, imagine a scene in which someone is about to be executed, and all hope of rescue - as far as the audience is concerned - is lost. Then, God's hand appears from the skies and picks the condemned man out of the crowd and kills the baddies. Deus is Latin for God, and the countdown caption is obviously a play on "expect the unexpected", so "expect the unexcelled (God)" says to me "deus ex machina", which says to me "Deus Ex".
Seems to fit!

Or more than one. The way they're hyping this up, it would have to be substantially larger than all of their current publishers.

Agreed, but there are single publishers that would be larger than all the current publishers combined, which is why we keep coming back to EA and Activision.

First off, that link is to the UK store, which doesn't help me much. Second, as echoed elsewhere, it looks like a rush job; it's easy to add "Vista Compatible" to an Amazon listing without it actually being true. Have you purchase this copy? Do you have experience with it?
Yeah, the existence of a possibly shady copy of the game on sale at Amazon isn't really the evidence against Planescape I'm looking for...

I know a few people have mentioned Sam and Max already - both the 'Hit the Road' classic and Telltale's so-so efforts neither of which really fit the bill. Since this is wild speculation, I just wanna throw '[url=http://en.wikipedia.org/wiki/Sam_%26_Max:_Freelance_Police]Sam and Max: Freelance Police[/url]' into the mix. The clues all still work (karmic awareness, different characters, yada yada) and it would be the biggest big thing ever AND 'unexcelled' (seeing as how it was never published, right ;-) )...

I'm still inclined to think that some Publishers would take exception to such fanfare and promotion of one publisher when their entry was just another day on GOG. They're saying this is the best thing ever for GOG. Which would be true enough of EA, but yeah, I don't know. There seems to me to be something other than that in the works.

I'm not sure what you mean... why does the counter need explaining?

Because thanks to the idiocy of both companies in the late 90's/early 00's EA and Activision hold the lions share of the IP's people on GOG are interested in.
Quite frankly either publisher would have GOG busy with releases for most of the year.

I've got it. It works fine with Win7 64bit. Although you naturally need mods to get the most out of it. It is a bit shady though as Interplay are selling it and they shouldn't be.

Because, as GOG told us, it counts down to the BIGGEST thing that happened to GOG since it's creation. Would Planescape be that? Not really. It's much bigger in fact. ;)

I agree, this kind of fanfare for a single game seems a bit over the top. That said, based on the wishlists compiled on GOG, Planescape is ranked number two and given the existing relationship with Interplay titles, seems ripe for the publishing.
Mind you, I don't actually think a single game deserves this sort of countdown fanfare, but how many of the top wishlisted games has GOG managed to publish so far? This would be quite an achievement for them, a symbolic release that lets us know they're listening and pursuing the very things we desire.
That said, I admit it's all a stretch... but that's what's fun about the guessing game, right? :)