I don't know exactly how Dark Anchors work in ESO.. but As far as I understand, they spawn in specific locations either randomly or at specific times.
I have a feeling that they will be really cool the first couple of times you fight to close the portal... but I also have the feeling that after doing a couple Dark Anchors, I'll just feel bored with them and just avoid them even if I see them.
I don't know about you guys, but I'd love to have a strong incentive to go rally ppl up to fight those Dark Anchors.. and I'm not just talking about cool rewards here.
I just have a feeling that a few months into the game.,. ppl won't really bother with them anymore because they'll be too busy trying to get some quests done or fighting at keeps in Cyrodiil.
To remedy this.. I think it would be really awesome if.. Dark Anchors are left unopposed, they start spawning more and more Daedras.. and they start invading the zone.. They may start occupying local towns.. where players might want to go turn in quests ect.. they could even eventually start spawning huge World Boss Daedras that will just roam freely. Something like this would really make players WANT to rally and fight at the Dark Anchors and prevent such a Calamity from occurring.
I'm not sure if Dark Anchors appear in Cyrodiil as well.. but if they do.. it would be really cool if they were used as a way to balance the factions. If one faction is clearly owning the other two factions and has most of the keeps.. Dark Anchors could start opening in that winning faction's territory.. and send waves of Daedras attacking nearby Keeps with huge "gate ramming" Daedras.. ect. So in this case, the winning faction would now have to focus on defending that keep and also have some ppl go fight at this Dark Anchor to close it.. which would possibly give the other two factions a chance to push forward and take back a bit of land.
Anyways.. just something I think would be cool. That's just my opinion though lol