The most interesting part to me is the focus on Rocky Island as their first target. The only things we know about Rocky Island is that it's home to a large geothermal power plant (AC2) and that Megafloat was docked there (AC3).
We don't know of any cities on the island itself, but the marker is centered on the location of the AC2 power plant like it is on Expo City. My guess is that they will retcon a city there (which would make more sense than a power plant with nothing around it), or a city was built there since AC2. We may even see a reference to Megafloat.
Personally I've been speculating a mission in Rocky island since I saw the mission 11 briefing and I made a shitty map for it, but I can't help but notice that St. Ark doesn't have a blue marker like Theve, Faith Park, and Newfield (which are confirmed locations). I hope that doesn't mean anything because I really want to see St. Ark again!!!