Praetorian Invasion Event?

Should just have part of the zone turn into a Battlezone and with more people in the area of attack have the attackers try and advance or something.

I love the idea of a Praetorian Invasion event but perhaps as another suggested, do it like the Winter Lord events.
Have the event start, little 'portal devices' drop all over town that you have to click during a time set. (like the presents) That spawn little bunches of invaders. Once you get the random amount, the main portal opens and in you go to face the War Walkers or something of that nature?

This way people with zone sweeps and Task Forces aren't interrupted on their own and anyone not interested can go on their way.

The only trouble I can see is the trouble with the random mobs being unleashed into the zone. Any thoughts on how that could be dealt with?