When viewed on a mobile device, this section isn’t blank … and piling too much data can cause issue. So I think I’d need to include some toggle capability to allow people to quickly hide a huge list of Challenges.
Also, as time marches on, I’ll need to limit/paginate that list… which can get a bit noisy. 
I like the idea of showing your rank. With some reason learning ( Ranking in profile - #10 by JamesChevalier ) I think I’ll be able to start incorporating the idea of ‘rank’ in many places throughout the site.