These are not business travel dates (Tuesday and Wednesday) and that is greater than a month out. Why are you trying to pick and choose discount fares when you said get rid of fare class restriction? You could already successfully use a GUC on most routes if you're willing to fly on non-business travel times, so why are you looking at these times?

As soon as you pick real travel dates (e.g., Sat->Thur) the prices go up to 8K. If closer in booking, it's higher. Do you know why those prices are high those dates? Because Delta will sell those seats at that price. Cherry picking dates in a market where Delta is non-competitive (no DL nonstop when nonstops exist) when b-class cabins are empty (Tuesday and Wednesday) is silly.

Maybe if you constrain your "super-GUCs" to Z fare availability I could see it as a not-so-crazy-option - although routes with heavy Z fare availability are likely to already be GUC-able today. But if you think for one second Delta is going to let you get unrestricted upgrades on seats that regularly go for 10K+, you are crazy.