Well, i wont lie: i too would definitely love to see XCom 2 (and its excellent expansion War of the Chosen) coming on GOG's warm sand shores.
I have the complete game (base, all dlc and expansion, on both PC and Xbox) twice, so, and yet i'd gladly buy it again here for the whole DRM-free creed...
But we have to face it: so far,the game, due to its 2017 Expansion release is currently still under heavy commercial exploitation phase; it was recently discounted as "deluxe edition" a bit before Xmas, the Tactical Legacy pack was also released.
So i fear the game is still too young and too useful, commercially speaking, for the publisher.
Plus the Expansion's ending is a sort of cliffhanger that leave enough space opened for a possible sequel later (a XCom 3 ?) but there were so far no announcement of it planned, currently in dev or whatever (maybe it's a big secret). So i wonder how long it would take, and/or what else it would take (sequel release, huge competitor release... ?) for the publisher to consider sharing it with GOG customer base...
Though it is true that 2K games recently had been quite generous and friendly towards GOG by bringing many less-than-10-years-old high profile games of theirs in the catalog here.. I already was overjoyced to see 1st Xcom reboot (EU/EW) to reach here, i really never dreamed to see this day...
AFAIC i wouldnt mind the base game Xcom 2 being brought here first, without expansion, and wait some time before seeing the expansion joining it in GOG catalog... Even if i absolutely love WotC, if it is the blocking point that makes us wait longer to get the game here, i'd gladly do without WotC for a while and be happy with Base Xcom 2 already (it is a good game even without WotC)