Specializing in Aerotheurgy will give access to Electric Infusion, Cursed Electric Infusion in the Summoning skill line. Any of these could make a great secondary skill line for the Conjurer.
There are several summoning abilities that a character will only have access to if they also have levels in a particular elemental skill line. One of the first things a Conjurer will want to decide on is if they want to specialize in a particular element. The conjurer already has an ability that would do well with several different playstyles but seems to be built to play a more supportive role in combat.