Official announcement from Cyan:
https://www.facebook.com/CyanGames
So what are we going to get new? And when its coming to GOG.com???

I didn't even know about this. I was tempted to start a playthrough of Real Myst recently, but I didn't want to deal with potential compatibility problems with Windows 7 that i've heard about. If this new version gets released on gog and works on Win 7 I may just wait and play it instead.

How many sales is gold?

Zero, unless you count pre-orders. ;)

"Gone Gold" means that the master files for the release have been completed (contrary to what the term means in the music industry).

Is it just a graphical/compatibility patch for the older game/engine, or completely new software?

After all these years I only learn this now?! Still so much to learn....

Probably the same difference between Myst and Myst Masterpiece:
http://forums.ubi.com/showthread.php/494717-what-is-the-difference-between-Myst-RealMyst-and-Myst-Masterpiece-Forums

Hopefully the framerate isn't as absolutely shitty on my computer as the original RealMyst.

Hopefully we'll see a realRiven at some point then. I preferred (and seem to be in the minority to do so) realMyst over the original game.

No, I can't stand the plodding clicking or FMV of either game, I much prefer the full animated, breathing and living world of RealMyst and Uru.

I think a RealRiven would be nice as well, seeing as apparently its so beloved already in slideshow form.

FYI, this will be a significant overhaul of realMyst. A much bigger change than the difference between Myst and Myst Masterpiece, but nowhere near as big a change as Myst to realMyst.

It uses the Unity engine (the original realMyst used Plasma), so it is an entirely new codebase. That's important for people having trouble running realMyst on modern hardware (although I can run the GOG.com version just fine on Windows 7, except not in widescreen resolutions). I believe it's based on the realMyst for iPad codebase (which also used Unity). It will feature a number of significant improvements like better lighting effects, day/night cycles (including Channelwood), a "point and click" interface (like the original game), and improved textures and more detailed scenes.

See realMyst: Masterpiece Edition Update.

So far they've only said it's coming to Steam. Hopefully it will make its way onto GOG as well.

As for realRiven, well Cyan haven't promised anything official, but there is a group of fans who have been working on a realRiven for several years now, with Cyan's blessing. The progress is pretty slow, but the stuff they have looks great, and is absolutely faithful to the original. See The Starry Expanse Project.

I have this on Steam, I will receive the upgrade for free?

Is it the same Myst as the original with updates or a different thing?

@Punished_Snake: I doubt it, but I don't actually know (Cyan hasn't talked about pricing). This is a completely remade game (compared to both Myst and realMyst) so it isn't so much an "upgrade" as a remake.

@MaximumBunny: It's the same basic game, with Myst Island and the four other islands you get in Myst, but it's in real-time 3D. There is also a new Age at the end (Rime). (Note that there is not another new Age in realMyst Masterpiece Edition; just the Rime Age that is also in realMyst but not Myst.)

I've already bought the game three times, if they want to wow me they should use unreal. Those pics look like a marginal update at best.