The Steam page of the game has been getting updated regularly this past few days with a bunch of different characteristics like achievements, language support, and even confirmation of "partial" but present, controller support.

Will the gog version of the game have all of these features?

I can't see why it shouldn't given that it's essentially the same version releasing on Steam, right?

I don't know the answers to your questions, but I definitely support your point.

No way I'm ever buying this unless it first given 100% parity with the Steam version in all possible ways, and also has zero cut and/or missing music.

I'm waiting to buy this game here on GOG when it launches with all the "upgrades" that comes on Steam. I hope it doesn't get too late...

Still no sign of achievements having been added.

After insisting for weeks and weeks, here's what an Aspyr representative replied to me regarding Stubbs the Zombie achievements:

"Hey there, unfortunately, we will not be adding achievements to Stubbs the Zombie on GOG at this time. However, we do recommend you reach out to feedback@aspyr.com so that it's made note of there too :)"

While it may not do any good, I recommend everyone write to that email to let them know how ridiculous they are.

I sent them a two paragraph email. Hopefully they'll add it back into their pipeline.

Thanks, maybe if they get enough emails they will change their mind, I hope for the best.

What situation with Achievements? Are this feature already available in GoG version or not?

No, it still hasn't been added.

Can we make a conclusion that the game was abandoned and all promises about achievements, controller support, and other features are forgotten? If so maybe it is time to delete the message on the game page "Achievements to be implemented at a later date." It is so sad that developers are not common visitors in the forum section... Maybe in case, when all developers visit the GOG forum more often - specific profile made for their game (or games) they make much better progress in updating and upgrading their games. Who knows...