DC_vipeout: As I wrote in the "Apologies" thread - everything will be released at the same time. The DLC will be released here as well. It's just that Steam has news that the developer can publish about the game and there's nothing similar here, as far as we know.
Hi there.
Released 16 minutes ago! Are there any plans for a secondary story for the Saracens or another DLC in the future?
As far as announcing future releases, there is a news section on the GOG Galaxy Store page, titled as "Coming Soon" followed by the name of the release. Otherwise, TBA (to-be-announced) DLC releases can be displayed at the main game's storepage, under the "DLC" section, linking to the DLC's storepage, without a price, but with videos/screenshots and a description (like a released game, while they can also be added in the user's whislist and "now released" notifications list).
Thanks for the timely release DC_vipeout.