Elmofongo: The Epic Games Store Exclusivity will expire in February 2020 and will be available in Steam as far as I know.
But was the game also planned to come to GOG?
I think if GOG was confirmed they'd have a "Coming Soon(tm)" thread by now.
Personally I have some decent hope because GOG got the previous two, and Deep Silver/THQ Nordic and GOG seemingly have decent relationships, and GOG must know Metro Ex would (imo) sell gangbusters here (compared to many indie titles).
Maybe it gets here a few months after Steam (after the initial sales period, maybe they'd be comfortable with a DRM-free version); would be unfortunate for GOG's sales but at least it'd come here. Have the game been cracked yet?
Also not to be rude but you've been here since 2011, so you must know (at least somewhat) that the rest of us forumites rarely know more than the others. Keep track of what's discovered and ask about games in the "unofficially confirmed" thread.