As far as I can tell, ironhide's games on GOG as of now are on par with their steam versions (please tell me if this is not the case), but the hammerhold campaign dlc for vengeance is not on gog. Are there plans to bring it here? I've been interested in kingdom rush for a long time, but I'm not about to buy any of them if the developers don't keep their drm-free version on par with the steam version.

Like many DLCs, the last free KR:V expansion took a month or two to make it to GOG, for whatever reason (the dev prioritizing other platforms, GOG's standards demanding they test it before supporting it, etc). I expect the same will happen with this one.

They just added the DLC related achievements, so hopefully it's finally coming!