It's a bit too early to be doing that, I don't see any point of requesting them to add a game which is at least a year and a half away.
I don't know why it would be. GOG is doing recent and even new releases these days.
Even if it is somehow too early, it's not too early to start getting Eternity votes on the Wishlist for whatever day isn't too early.
If only this were so. The off-line mode has only ever worked for me when I don't need it to, i.e. when my internet connection is intact. Trying to turn it on whenever I actually need it because my internet connection has gone down, it refuses. (So, yes, I could run in off-line mode all the time... in which case I lose all the networking features that provide a carrot to go with the stick. Good job, Valve.)
I do like Steam, it's the best I've tried as DRM clients go. It certainly has its uses and I've bought a lot of games on it. But due to the downsides, I often view it as more of a bargain bin, unless someone forces me to it as a first choice by using Steamworks.
As others have said: if you like Steam, that's great. Obsidian would be fools to not put it on there, and I'd happily lend my vote to Eternity on Steam Greenlight if it needed it. I personally would prefer to be able to get it under a lighter DRM system (preferably none at all), and from this thread it seems clear I'm not alone.
You win the Nutshell award, good sir/madam.
"DRM free" is certainly more important than "on GOG." (Though one of the things I love about GOG is that the latter ensures the former. Any other game shop makes me do research just to make a purchase.) If the latter is not doable, I'd still be pleased with just the former. But I do prefer GOG, just so I have a service where I know I'll be able to go redownload if my local copy fails - as opposed to a developer's server subject to the fortunes of that particular company. It's like Steam without the disadvantages.
And yes, you are correct, it is just like the reason Steam users want the game on Steam. So I'm glad you understand us GOG fans.