In very basic terms: modules and weapons generate threat; as the threat goes up and down the NPCs will change targets and allocate secondary targets.Threat? Threat? Where did I hear that term before...? Oh yeah. And here. And here. You get the idea.
It shouldn't be a surprise that Eve is implementing it because its a successful mechanic as evidenced by how many other games use it for their NPCs in order to create something more than mindlessly attacking the first person on the screen as Eve does now. I'm slightly concerned that having groups manage threat so the DPS and healers don't get aggro from the tanks might create a new "holy trinity" way of running raids into Sleeper space that is far too familiar across the MMO genre. I'm concerned because instead of making PvE more like PvP, they might just make a new form of PvE that is based on the "holy trinity" and "managing threat" mechanics and will not do anything to make players ready for real PvP.
That being said, it remains to be seen what this all shakes out as. Since Eve does not allow third party add ons, perhaps managing threat without them will prove to be too difficult, and the actual mechanics for generating threat might be very convoluted and hard for the average group to control. Perhaps it will be enough of an evolution from old mindless PvE to move players closer to being able to PvP in the same groups and ship fittings.
Regardless, time will tell.