...long term mod support for the GoG version of KCD2.
Yes, the game will support mods, but I think the only source of mods for Gog-users will be NexusMods (or other random sites), while WarHorse will focus the dev-kit and official mod support via Steam Workshop,
And if only valid Steam users would be able to download from Workshop (like most Studios choose to do it), gamers will have a 2 tier modding community, where on community will be vastly superior in knowledge and skills. Some mod-authors will upload on both sites, but over time that will shift...

Just look at Baldur's Gate 3. After official support was released September of -24, and "forced" the use of mod.io, the number of old and outdated mods increased (and new releases decreases) rapidly on Nexus.

I hope I'm wrong.

mod.io is a good modding website while nexus abuses their monopoly. (Reember how they changed downloads to needing an account, introduced collections and force the use of vortex for them. Etc.)
I do hope that Warhorse uses some third integrated modding system like mod.io.

Steam Workshop is not great but you can download the mods from there using steamcmd or shadoxxhd /
steamworkshopdownloader.

Mod.io vs Nexus wasn't my point. My point is that when Studios "forces" one platform, authors over time will pivot to that platform, because it takes more time and energy to maintain your creations on multiple platforms.
And Steam Workshop over steamcmd isn't very user friendly, is it? And many Publishers will not allow access to Workshop with an Anon login, or with a true steam login with out purchasing the game.

Definitly agree with you, I think a good solution would be an interoperable industry standard so you can just switch to a different mod repository seamlessly.

Yes Steamworkshop over steamcmd is hell.

Well... sadly, mod.io is not a "good modding website" at all... It's no better than steam workshop. :(

In fact it, as well as similar undertakings like Thunderstore and so on, is prettymuch exactly like Steam-Workshop, and the next big cancer infesting the gaming community.
Because those are just one thing: mod-DRM... which is also the reason so many of the bigger game-devs embrace it, sadly.
They do not offer anything noteworthy for the actual modding community, to the contrary... they only provide regulation mechanisms for the devs, by the means of a cetralized forced infrastructure. (yes, that is exactly the very thing steam is...)
Remember when Bethesda tried to force their CreationClub on the modding community? What did they most notably do...? They released meaningless mini-update after meaningless mini-update, just to break the free mods with uneeded changes. Thankfully, they did not succeed, because of their image damage, and already established modding structures.
Now... entry: mod.io ...
Even more perfidious, they outsource that modding hinderance to the (so far mostly oblivious it seems) modding community. With the restriction of mod accessibility, devs don't even need to bother about changing their game to break free mods... the modders do it for them with their very work.
So far they are a paragon example for the "Embrace, Extend, Extinguish" strategy.

Because of that I'm highly dissappointed Larian went on that route with BG3... :(

The part around NexusMods is sadly simply true... the typical god complex they developed in their niche led them to now lose the foothold they once had. Others are more restrictive and thus appealing to DRM devs... and for all others, their service is now no real alternative anymore.
I just hope, they realize that problem and tackle it by adding a speciality to their platter the way they did more than a decade ago... a truly free modding platform.

I don't have too high hopes though...