This will go into effect for the matchups beginning on the 31st.
This is the happiest thing I have read all day! The original post was light on eta details, and I immediately went into panic mode. I am one EB Overlook vista away from world completion, (and my legendary) and I planned to get it tomorrow when Blackgate dropped to red. Whew!
In related news, I support this new system as a huge step in the right direction!