A few of us were talking in the chat about how control fields should give all those who have a resonator or link credit, and that you should get some kind of time AP credit. Maybe a time bonus for keeping a control field alive every 12 hours or something like that. Nothing large, but definitely an incentive.
Also, it would be nice to have enemy portals underneath a control field decay faster, while friend portals decay slower. Again, more incentive to destroy enemy fields and deploy your own.
Lastly, XM would be decreased for enemies underneath your control field, and be more plentiful for the deploying team. But I think that might give higher level portals with high shields too much of an advantage if you cannot find enough XM to power your XMP bursters. Imagine a LV8 player trying to take down a LV8 portal...you lose soo much XM that you would only be able to fire a few bursters before having a red screen of death!