The other way China can extend its anti-ship ballistic missile capability is to take the DF-21D and deliver it to launch points far out to sea via aircraft. Although having heavy aircraft launch ballistic missiles is not common, it is not unprecedented.
The idea was toyed with during the Cold War and today C-17s drop ballistic missiles as targets for anti-ballistic missile tests. Still, there are no operational combat systems that do this, but then again the job of creating a giant anti-access bubble around one's country and attacking ships with ballistic missiles is somewhat different than using the technique to launch traditional nuclear-tipped ballistic weapons.
http://www.thedrive.com/the-war-zone/13511/is-this-chinas-df-21d-air-launched-anti-ship-ballistic-missile-toting-bomber