Personally as far as the cover goes, I like the black and red style that currently dominates the site and artwork; don't enjoy the blue addition as much. I think that simply the Kol's silhouette (the current logo for sins, possibly with more emphasis on SINS than on 'of a solar empire') in front of the red volcanic planet would be a perfect cover. It's obviously space-related, and will visually separate the box from other, lower quality, space-themed games. It's simplicity will hopefully be intriguing, as opposed to a spatially confusing blob of ships as is currently.
Also, I thought the phrase "Times of war are upon us" was powerful in the trailer. Perhaps it would make a good box caption as well?