I see where your coming from, but the community activities hub truly is where competitions would really fit in.
"Community Activities Hub
A place for the community to advertise activities and events in and outside the game."
Competitions would fall under this ^
Sadly not many community hosted competitions are posted nowadays, so creating an entirely new child board for it to remain empty aside from one or two posts I do not see much a point in making, for now. If the activity on these competitions were to pick up, I could most definitely see reasons behind it then.
Either way, I do like the idea.