My Ideas after completing all the missions on Auroa to keep people playing and to give us something to do (After raiding there is no point in doing anything so these are my suggestions)

A new operation on another Island (CIA sends him out solo due to the unusual activity on the Island n stuff) | You need to complete EVERY mission on Auroa before doing it, convinces us to play more.

Harder enemies and is further in future with Skell weaponry supplied for him to be tested for military use. Skell was used the Island for innovation but was invaded and nobody knows how.

Much more stuff people could post in the comments that might be cool