To expand idea further, implementing above idea will require a marketing story to go with it.
Idea is as follows:

We have recieved intelligence reports on a massive invasion by npcs who will arrive on alpha shorelines on xxx day. To counter this threat, we need you the player to join us Blah blah blah. Allow 1-3 weeks for new players to grow accustomed before setting up first invasion event. Hundreds or thousands of t1 fit npcs will arrive on alpha islands and start to converge on the main terminal from all directions. New players and vets will have to work together to stop invasion. If event is successful (assuming devs fix the lag issues) word will get out and more players will join. Set 2nd invasion a month after; same concept as first but more difficulty