hmmm that would be interesting, however there are already some regular photography contests / challenges on HIVE here. Each has theme/topic, the last two I notice are Gaming Photography (mostly open world high detail graphic screen shot) and Phone Photo contest (taking pic with our phone).
I saw you were on bike before, so I think if you start photo contest... maybe things that related to your bike is the better one... such us off-road course / dirt track, trail run course , mountain view or some walking path in forest... or maybe your ride, how you have modified and remodeled it, etc.
But better if you collaborate with existing related photography community first, because they have the network/people. just my 2 cent.