Well, if I remember well the expansion will be releases this 26/August, with the 2.0 patch, after this, is only the time that Obsidian will take to pass the patch to Gog and they to release it (Users using Gog Galaxy should get it very quickly, in theory).

Short answer: Begin to prepare the torches at 26/august

Its good to hear that the patch is comeing soon, but are you saying this is the only patch for PoE that is comeing out for GoG? So like in the future, eg: v3.0, will only be available for steam?

No, he said "is only the time" (ie, it'll take a few additional hours/days for the time for GoG to do their packaging and QA) not "it's the only time" (ie, after that no more patches). Patch will continue to come here, for all what I know.

Rock on, because I didnt wanna pay 45$ for another copy of the game just for patches and updates. Thank you for the info.

As Kilobug stated, futures patches will always be available in Gog,
Only possible exception: If Obsidian stop giving support o the game alone, and only focus in the game+expansion (But is unlike to happens)

On the official forum they said that it will be released anytime between the 20th and the 25th:
http://forums.obsidian.net/topic/80953-update-20-beta-is-live/?p=1719574

Given that today is already the 23th, I guess it's unlikely it will go out before the expansion.

Is achievements working?