In connection with recent events, why not introduce something into the game that could itself be transmitted over the portal network? Like a virus, from the game plague inc. For example, there is a huge cluster of enemy portals. I infected one portal and then the infection was transmitted to another portal and then another city or even several cities connected by links. And infected portals would discharge faster, or reduce the receipt of certain items ... Imagine how much it would revive the game.
It would also be possible to strengthen the portals of your team with this mechanic.