It is the second game from the creators of "Gris" which was rated very high, so obviously there are some expectations for "Neva". Both are rather short games (less than 10 hours) but indeed the "indie community" and the lovers of those atmospheric games are in a high favor for it.
I think the reason why it is not available for GOG on launch is probably a mix of 2 factors: They do not want to provide it DRM free any quick (yes, even Indie devs may love their DRM, this is not a AAA-"issue", it is just less likely to happen) and another thing is the usual rather limited sales (compared to the "we rule it all-platform") on GOG, so they do not see sufficient rewards for it.
Somewhat sad but simply how it is... yet i do not lose many tears because there are already more great games on GOG i could ever play (properly).