I prefer the original galaxy, if I keep the installer will I be able to use it in the future and keep adding my games this way?

As long as you uninstall Galaxy 2 it works just as before.
I'm wondering if they'll change this in the future when G2 launches.

Although I'll personally use G2 (as long as it ends up being as awesome as we're hoping for) it would still be cool if you could use Galaxy 1 if you aren't too keen on G2, that way they'll avoid what Valve is going through right now with the part of the userbase that doesn't like the new Steam library UI :)

I see where you're coming from, but maintaining 2 'branches' of programs that ultimately do the same thing in the end... it's taxing on the dev team. Even if people say the 'older' versions don't need any kind of maintaining, they eventually do. I particularly don't like Steam's new library for example, but I don't condemn them for "imposing" the new one to all users. As, I'm afraid, GOG will do eventually with GOG Galaxy 2.0.

That said, ask away as a feature! They might change their mind!