You can pre-order the game on Steam and receive exclusive content that isn't available on the GOG.com release, precisely because it cannot be pre-ordered - the bonus traveller skin is minor, sure, but shouldn't GOG users be able to get it too if they so desire?

I mean Im no expert but maybe they are getting ready everything for the other game sites. Like getting the achievements and the files ready on the major 4 (Steam, Playstation, Xbox and NIntendo(if they release it on switch 2 at the same time) and then implement it on GOG. Might be wrong, but im glad GOG is getting this game to be sold here

It's good that the game is at least sold here. But who knowy Maybe the Bonus Skin will be available after Release as well, who knows.

hopefully

It's clearly trying to go for the aesthetics of Dead Space so the marketing of the game should be geared towards that.

There is a Launch Bonus till September 8th, that might be what the Pre Order Bonus was
The there ain't many details to it

I can Confirm that the Launch Bonus is in fact the Pre Order Bonus

Great to hear, thank you so much for confirming!

Tho it was only available if you Purchased the game before September 8th