Senteria: You guys bring up Undertale as an example. Let's look at a different example: Stardew Valley. A massive success launched Day 1 on both GOG and Steam. So it is very possible to get your game day 1 on gog. Stardew Valley is developed by 1 person and if only ONE person can get a simultanous release why can't more?
zeogold: How was the hype train on it running before release, though?
No Man's Sky had a day 1 release too, and look what a fiasco THAT was.
Stardew valley had a small following before release. Then the hype started when it was released and people really liked it. It wasn't that well known at all. To me it randomly appeared on the gog page and I bought it day 1.