Yeah, no thanks from me.
It takes less than a second for me to see a duplicate and ignore it. Many times a duplicate is actually my first encounter (I'm not on here 24/7, reading every single post).
There's also a pattern of visibility problems with some posts, otherwise there wouldn't be a second-chance pool -- good quality posts that are posted at the wrong time or whatever -- and you want to punish those users? For having a good post that didn't get lucky enough or wasn't posted at the right time?
I guess if you want to massively reduce the number of submissions (including many engaging and topical posts) this would be one way to do it... Not sure it'd bring the results you're after.