No, I think you'll be stuck with it for 8 weeks. See the article at Reaper’s Rewards Event | EA Forums - 4967458. Line #7 in the numbered list says,
The Reaper’s Rewards Event will have six weeks of Quests and two extra weeks at the end, so there’s plenty of time to catch up and complete it!
I think the best thing to do is complete the challenges if you don't want to look at them. The challenges get removed from your screen once they are completed and this week's challenges were pretty simple. Of course, you'll still have the icon for the event but that's easier to ignore than a task list.
I don't know why there isn't an opt-out but my guess is that it's probably because the developers didn't expect many people who wouldn't want to get free stuff.
The free stuff is great for those that want it.
I don't want it and I would like the option to opt out in the future.
Marketing and hype for the new EP.
EA really needs to up their game. I feel like a base game EP is coming our way after 10 years of play.
