Increase the "Ask Question" Privilege Threshold to +10+2
I should note that I'm not convinced that this is a good idea but I figure I'll mention it to see how others feel.
On Q&A sites, the point of posting a question is to get help, to ask a question and get an answer. There shouldn't be a barrier to asking a question. However, in the context of creating and posting challenges, there are many more things to consider.
For this reason, it may be a good idea to require some familiarity with the site in order to post a challenge to the main site. The easiest way to do that would be to require potential challenge authors to have earned at least 102 reputation on this site before being allowed to post questions. This would require one upvote on one answer or one accepted edit. Note that "on this site" implies that an association bonus wouldn't count toward this privilege.
This would also help reduce the number of blatantly off-topic questions we get.