And let's not forget about popularity. If GOG made a client which can be directly influenced by 3rd party companies and individuals, we might just get something to (extremely slowly) start rivaling Steam. Imagine: A developer who's working on his game can introduce a brand new feature to the client, as long as it's not an attemt to protect his product.

Well, if GOG appreciates the potential of such collaboration, they can team up with Humble Bundle, Desura and others on creating such client. But even if they'll develop it alone but in the open, it will be a huge advantage over Steam.

I'm fine with closed source as well, just as I am for other digital stores. Up to GOG if they see any advantage making it open source.

GOG does not owe it to anyone to make it open source, anymore than those other stores.

I'm not really "pro-linux" (whatever that means) but I would like to see GOG release games for that platform. And I've no idea what that has to do with anything?

Of course they don't, that's the distinction between 'requesting' and 'demanding' :-P

I don't use any closed clients from other stores. So it's good that GOG keeps the client optional. But making it open will positively differentiate them from others. It's in line with GOG being DRM-free.

I saw this thread, found the request beneficial to the gaming community and wanted to vote...
just to realize I already voted for it in the past. :)

Just to be clear on my personal position (as distinct from shmerl's):

I don't care about GOG's client being open source. They can do whatever they like with it. As long as there is official support (documentation, etc) for the GOG community to use the same APIs.

As I said on the other thread (http://www.gog.com/forum/general/third_party_clients) I'd like the GOG community to be able to make it's own client. shmerl could even make an open source one. Someone could re-invent the light-weight GOG Downloader of yore. So long as GOG provides the APIs for us to do that we can be sure DRM isn't an issue.

Official and documented APIs would also mean no more having to scrape the website if you want to make a GOG search engine. Or create an app that uploads your profile to the Wiki. Or whatever else the community can imagine.

There are actually two requests. You probably voted for opening of the client. This is a more recent co-request to open / document the protocol (so if you didn't yet, please vote there as well):

https://secure.gog.com/wishlist/site/document_the_protocol_and_api_of_the_galaxy_updater_client_to_enable_community_alternatives

...but has nothing to do with it, really. When I download DRM-free GOG games with the current, closed source, GOG Downloader client, the games are still fully DRM-free.

It has a lot in common with it. Namely trust. One of the aspects of DRM is that it never can be trusted. Improving trust with opening the client is in line with being DRM-free.

Maybe it is just me, but from the earlier linked discussion, I got a bit of the entitlement vibe, as if GOG somehow owes it to "us" to make their client (or APIs) open source.

Has any other PC gaming digital store made their official client or API open source? Humble Bundle offering torrent downloads with open source bittorrent clients doesn't count, as they are not doing any development for bittorrent. They are using existing technology, just like GOG is when offering http downloads (without a client).

They are two unrelated things. Having an optional "closed source" client does not in any way take away from the ideals of offering DRM-free games. We already have a closed source GOG Downloader client, yet the games are still DRM-free.

But Galaxy is so much more than just a download manager. Management of online multiplayer matchmaking? This is an area that gets quite close to DRM, does it? Will users be able to turn off automatic updates, even for single titles? Will they get the installers updated or the games? Can I turn off the bloody achievements? The problem is that you get all in the bundle with Galaxy.

DRM is a all about control and I can understand fears that a mighty client could mean losing some control. On the other hand one should wait until this really happens before accusing someone, right.

If the Galaxy client turns out to be much better than the Steam client I wish it a wide adoption, and even for that open source could be beneficial. It's just a request pushing GOG a tiny, tiny bit in a direction I think is favorable. I support it.

Desura was supporting the open Desura client: https://github.com/lodle/Desurium
Not extensively, but they were involved.

They are two trust related things. Having no DRM improves trust. Having open client improves trust as well. Here is the relation.