Here's a reply that a similar forum got from an Opera forums moderator: "When a version with that feature is released, then we will know." Very astute observation, I'll say. A thread in which they decided to close right after saying that.

If this is the type of attitude they have for adding one simple feature, thats already in their other browser, I'm not feeling too confident theyre gonna add it to GX anytime soon. They advertise the tab islands so much as a main feature for Opera, if they added it to GX then that browser wouldn't pull as many users. You would think they could pull just as much users in, maybe double, by advertising that feature in both browsers but unfortunately not.

Either way, my teeth will be grinding everytime I see Opera advertise their 'quick and sleek' tab islands feature towards me, when Im already using a browser that the same company has made but refuses to implement the feature into.