Apparently GOG is taking the 'Connect' feature one step further and will allow all games from other launchers (and platforms? didn't see details on which ones yet) to appear under one library in the Galaxy client. This also includes friends & chat and achievements (!).
It seems that cloud saves & auto updates will not be supported for non GOG games.
I've seen other software trying to do the same thing & unite all (or most) PC launchers under one roof but this seems like the most serious attempt to me.