User blog comment:Kushieda minori/Game Update note May 10, 2016/@comment-151.29.93.215-20160517171510/@comment-27652489-20160518141228

You probably need both Airship Docks @ lv10 to buy the remaining Kingdom expansions. I've got 1,258,000 resource storage with all lv10 storehouses & 1 lv10 Airship Dock, another lv10 would make 1,358,000, so I don't think the Kingdom expansions would go much higher than that.