I was watching a twitch stream, and the streamer was playing IWD:EE, but the interface looked different and improved.
I asked if he was using a mod, but he said he was using steam, which has had the new 2.5 update for a short while.
Checking my GOG version it is only 1.4
Do we know when the new 2.5 version will be available on gog ?

It seems that Steam users had the chance of beta-testing v2.5 with the option to report bugs, etc. up until the January 15th. My guess is any reported issues will be ironed out and then the update will be released here. Although six weeks does seem quite a long time to be squishing those bugs - maybe there were quite a few of them... :)

http://steamcommunity.com/games/321800/announcements/

Latest news about 2.5 version are here:

Regarding BG:EE, BGII:EE and IWD:EE - the 2.5 patch is going to be in the beta for a bit longer. We’ll be updating it with new languages, localized V/O, features, and bug fixes soon. We’re giving the translation teams a little bit more time to get their updates into the games. Expect to see a new build in early March. I think when it out. There is no ETA at this time.