chrome nova
In bf3 was good practice to give super-achivement every 100 kills or every N hours of playing some class.
Its unlimited, you got 100xp per kill for example, and every 100 you got full screen medal - and instantly 10000 xp (for that amounts)
Personally for me xp is useless, but if you believe to... Killing people with pistol and sledge hammers should be non-required, but marked with medal that you could see (and show to friends) via player profile / web-page (story about bipod-knife)
Actually weekly tasks should force players to do something that they dont want to do. Healing, repairing, capturing points, resupply ammo, that stuff for every week teamplay include.
I'd recommended to create mixed gamemode with several tasks that is become cross-squad - 1 squad gets task to plant bomb, 1 enemy squad - gets to disarm that bomb, 1 squad - capture 3 points, 1 enemy sqaud - protect 3 points, and that all will mixed with some variant of ffa - any squad could accidentally break task of other squad. I mean - random task generator.
What is win condition? Hmm. Maybe initially each squad has 5 tasks on the map. Once solved you squad get access to unsolved tasks of any other squad. Once all tasks is done - team win.
So your daily gameplay would be "solving tasks" instead of fight inside the mess for control of one point, that will be captured minute ago by opposite team.