For example: If I own games twice over different platforms (like on Steam and on GOG (through GOG Connect)).
Will Galaxy 2.0 recognize these games as the same and merge them somehow with their playtime etc. Or will they be handled as two seperate different games?

Same games on different platforms will show up as separate entries in the library, simply because they are on different platforms and possible achievements have to be tracked seperately per game.

However, GOG tries to merge the gametime. It just gives you a total gametime in hours and when you hover over the total it breaks it down into the seperate hours played per platform.

This sounds cool! So no more double gametime tracking? This would be great, I always try to sync between GOG and Steam. ^^'

Technically it still does track them independently because it just pulls the info from your linked accounts, but on their own page (which has a 'friends-leaderboard') it shows the total amount of time played for both accumulated as I said before.

So If you play the Steam version of a game it will increase the game-played for the steam version, not for the GOG version, and the other way round. But it will give you the total hours played based on all platforms on the game-page.

Example: My played time for ''The Saboteur'' on GOG/Origin both show 31 hours 20 min of played time, but if you hover your mouse over the time it shows 2 hours played on Origin and the rest on GOG. (which makes sense, the origin version is broken and I haven't touched that in forever)

Thanks for the explaination. Then I should really stop to double-record my gametime. This is what I currently do, if I for example play Duke Nukem 3D via eDuke32. I replace then eDuke32 with the Megaton Edition on Steam and additionally I start the DOS version via GOG. This was back in May, when Galaxy 2.0 was not announced yet.

So I will stop with that and let the platforms record indepently. :)