Coop is fine, apparently, but open play has lots of griefers, at least at the start.

From what I've read you can set your network settings so other players can't damage you or your structures. But that doesn't stop people from griefing in the form of messing up your base with their terrain manipulator.

I honestly don't understand what exactly HG would need from the client.
It's able to give access to your user data (name, but does it need more?) A text channel should be foreseen by the game itself, location too. From what I see lobbies are possible using galaxy.
I did hear that it can't give voip, but that's not really necessary?

But what features are those? I run NMS through Galaxy and as far as I can tell multiplayer is the only thing that's different from the Steam version. Everything else (cloud saves, 'cheevos, time tracking, etc.) all seem to work the same. Perhaps there's something in galaxy that makes it difficult to do multiplayer, but I find that a bit suspect since there are other games that use Galaxy for multiplayer without issues.

Seems both parties are pointing the finger at each other. All I know is HG said they'd have multiplayer for the GOG version by the end of the year, implying that Galaxy can support it. Also implying it's not actually GOG's fault. I don't know, but I think it's likely a little of both: HG probably concentrating on other things and making GOG multiplayer a low priority, and Galaxy maybe being a little more difficult to work with than HG was expecting.

Considering the multiplayer capability (or lack thereof) of other gog/galaxy games together with gogs open and humble communication approach (...or lack thereof) I would point fingers at gog/galaxy as the culprit. All fingers. And toes too.

In theory. Practically I do not care enough for that (multiplayer). Although I did pondered buying NMS as a gift for 1-2 peeps I think might be interested in it and occasional small time MP with friends & family; but I don't do that on a wudda/cudda/shudda/mebbe promise. And of course I will not do it on this Steam thing I keep hearing about.

No, they said that they expect to have mp for gog by the end of the year. Not the same thing.

https://www.gog.com/news/no_mans_sky_next_update_now_live

And the sentence about "joining forces" with gog to introduce mp suggests that while it's theoretically possible that galaxy could support mp, that might require changes, i.e. it can't support it presently.

Difficult to say whose fault this is.

NMS seems to be taking advantage of existing multiplayer capabilities on the other platforms it's been released through. That is fine and sensible. Especially with such a small development team and for a game which doesn't charge a subscription and hasn't charged for any of the major updates.

HG did flag their intention to introduce exactly this style of multiplayer long before launch. Presumably gog would have been aware of this and wouldn't have agreed to sell NMS if they weren't willing to support it. But we don't know that for sure.

We also don't know what kind of costs would be involved. Xbox and PS4 charge a monthly subscription for hosting multiplayer. Not only because they can but because there are genuine costs associated with that. Gog might understandably not be keen about shouldering those costs for NMS.