This actually has nothing to do with the upcoming Crossover comic.

To commemorate the 100th issue of "Generation One" comic, and the 200th issue of the "original" GIJoe comic (coincidently, both are being released in March), IDW are producing a group-shot image that will be split over those two issues. (but are just the incentive covers, which will be hard to find cheap)

The combined image of both covers can be seen here on the artist's site.