That's a shame, do we know why? is it just not finished being implemented? I found a page[0] that said at some point they had stalled on refactoring something.
[0] https://ghc.haskell.org/trac/ghc/wiki/Records/OverloadedReco...
[0] https://ghc.haskell.org/trac/ghc/wiki/Records/OverloadedReco...
tl;dr: The patch worked but was messy/overly complex, so it needs refactoring before it's merged.