I expect it will taper off as it progresses. Some will see it's been going for a while and figure they'll wait for the next one. Some existing contestants will see something shiny and wander off, never to be heard from again. I fully expect there will be about ten regular contributors at the half-way point, which is very easy to keep on top of. I can make it really easy and only do an update on the table at the end of the month, which is what I'll probably do after three or four months.
But yes, I think it makes sense to put up a hard deadline.
All y'all fence-sitters, yer on notice. You've got until COB (California time) 10 Aug to make your entry. After that you'll have to wait for the next Magical Mystical Fastlane Competition®.