The title says all. I bought the witcher 3 on steam as soon as it was available, long before release and when there was no GOG galaxy.

Now, I rather support GOG when it comes to buy the expansion pass. But if cannot get my steam version of the Witcher 3 on GOG galaxy, I'll have to get the expansion on steam too.

That's a bit lame.

(note : I managed to have both the witcher and the witcher 2 on GOG from steam CD keys, so I'm not really asking for something really)

Buy the expansion pass on Steam. I doubt you will be able to use GOG's expansion pass for your Steam version.

To the question: how not to buy the season pass on steam, your reply is do buy the season pass on steam. Hum.

I do think it's in best interest of CD Projekt to make this possible.

Maybe they will do so years later, maybe they won't. The way things are now, buying the expansion pass on GOG will lead to nothing more than a waste of your money.

CD Projekt RED wants gog.com to compete with Steam.

I hope CD Projekt RED never lets you get a gog.com key if you purchased The Witcher 3: Wild Hunt from Steam.

Sorry, but CD Projekt RED and gog.com deserve all of the money that they can earn from selling video games.

So you mean by this: you hope that CD Projekt would not be helpful to me despite the fact that I supported the company:
- by starting using and buying games on GOG two years before you
- by buying their games more than one year before their actual release
(not sure you should be patronizing me about supporting CD Projekt)

I do not think that's the spirit of CD Projekt/GOG not to be helpful to users. Especially not to users since years support their work by buying theirs games, no matter where or how.
I think CD Projekt/GOG can compete with steam/origins etc in a much better way that what you suggest: not by punishing users for X or Z reason but by providing a better service.

Maybe I was not clear enough: my question was directed to people from CD Projekt/GOG. Not random average player that knows about CD Projekt since 3 month and thinks as an odd zealot.

You won't find CDPR staff members here. Your best bet for that would be the CDPR forum. As for GOG staff members, they usually don't respond to forum posts except for technical issues and announcements. If you want an official answer to your question, you should contact GOG support.

I started using gog.com on May 18th, 2011. This is not my main account. I have 3 gog.com accounts, this is my main account for talking on the gog.com forums.

I actually did both. I thought that there could more than one player interested in this and was wondering if someone already asked and got a reply about this.

May I ask why you need three different accounts?

No official reply as far as I'm aware of.

Because I can have 3 accounts if I want to? To purchase video games on all of them and support gog.com more to break Steam's monopoly.

Just like when I purchase 2 copies or more than 2 copies of the physical boxed versions of the PC versions of video games.

You cannot purchase the Season Pass on either store without owning the base game, so cross-platform purchases for the same game would not be possible.

You actually can purchase the Season Pass on GOG without owning the base game here. Presumably, it was done this way to allow people who bought the retail version to be able to buy the expansion pass before the game's release (though, it's redundant at this point, as the game has been released and the retail version comes with a GOG code anyway).

Would you be able to download it directly? In that case, for the OP of this thread who asked the question, yes, it should be possible.
The Witcher 3 is DRM free on steam (or so someone somewhere else on these forums said), so if you bought the season pass here and the base game there, you should be able to install the DLC somehow and play it.