Gaia Unicron is a TFPrime/Arms Micron figure that Hasbro have said they have no plans to release (at this time), and since it is a character from the cartoon, this will interest collectors.
The concept seems a bit odd though, almost as if it is a gimmick forced on the toy (and you know how that goes, spoiling the toy). The concept is that it merges with an Optimus toy, something that didn't happen in the cartoon, and doesn't make any sense.

The image is probably a place-holder/mockup, but it lets us know to expect a more expensive 2-pack, instead of just the Unicron toy on its own.