Do you mean that it's possible to add everything to Galaxy, in theory? :O
Even Steam? XD

In theory, yes.

Not just in theory.
An application of galaxy includes launching steam via galaxy.

Can you add GOG Galaxy to Galaxy? If so, can you have two instances of Galaxy running at once?

Hmm, intriguing. What could possibly go wrong?

Obligatory... Galaxyception! :O

Do you want to create worm hole?

Well, on my Linux system, I can start Bash from Bash, and it is the norm to be able to run arbitrary many instances of any given program.

Actually I was killed by unknown German soldier several times. Not to mention, one of Bethesda's members jumped out of the window seeing me playing Return to Castle Wolfenstein with Galaxy. So, it's not like no one gots hurt because of my cheekiness..

About a year and a half ago I was *previewing* a GOG game borrowed from a friend
(I later bought the game making it official)
During the time I had the borrowed game installed Galaxy detected it and added it to my library
listing; or at least the section that showed what game I was currently running.

I don't know if this has been patched out but at the time, suffice it to say; Galaxy could see it

This interests me, it's been a looong time (university undergraduate) since I last pirated a game. These days games are cheaper (thanks GOG), I have more money, but less time to play.

When I do buy games, I'd rather buy fewer, better games which I pay for at full price to support the Dev but after paying for POE and being very disappointed it has put me off buying games again, at least at full price.

It'd be nice to be able to borrow / torrent a GOG game and treat it like a demo. If I like it then I can download it officially (at full price to support the dev) and keep on playing at the last spot (due to GOG galaxy synching saves).

Thousands of FBI agents burst into your house and point guns at you! [/definitely joking]

The bigger problem is galaxy autoscanning your hard drive without permission and slowing down your computer until it's finished.

you all jump on the bandwagon of "oooh, you pirated a game" but there is a LEGIT situation i encountered that didnt involve pirating or borrowing whatever and where such question was a valid concern

Dragon's Dogma

Dragon's Dogma has an online multiplayer feature that allows you to borrow the secondary custom character of other users to add it to your party (your party has two free slots for that out of 4 party members, the two others being for your own player cha&racter and your secondary custom character known as "Pawn")

When i used to play Dragon's Dogma on X360 at its release, i quickly ran into a problem: basic offline paws are weak and poorly (if any) optimized in perks and skills, and ill-equiped regarding gear. I had no friend to play or share with, and i reached a point (very quickly) when regular users pawns were either too weak, or they belonged to very advanced players that made their pawn's recruit price too expensive for me in rift crystals (the currency for MP borrowing)

I was on X360 so i made two other accounts on same console, i began to play two concurrent additional playthroughs of the game (i liked it and didnt mind) and could test different play style and look for both my main chars and my pawns... And in each concurrent playthrough i'd recruit the pawns of each two other accounts. That way i had complete control on which characters i was venturing with, optimization and such.

Then came the GOG version, and i am left wondering if i could ever do the same, meaning create two additional accounts and use all my accounts on same computer with game installed with galaxy and recruit my two other account's pawns or not (without purchasing the game 2 other times for each two other accounts)

If galaxy prevents me to do that, and especially as the MP player base for the game on gog only side is waaaay smaller, i would end up having Galaxy limiting my game experience and possib ilities harder than any DRM, and harder than a DRM-ridden console ever did
... incidentally ending up with galaxy/gog version more limited by DRM than console version... which is sad and odd

i suppose there are other situations involving gog games and galaxy where legit concern not involving piracy or whatever could arise...