I'm sorry, I completely disagree with this idea.
I am someone who uses the fighting zones often and because of my status there, I get asked for fights by all levels and I don't mind that. Plus there are people like my student, Aekanaru, who can fight Hokages and some Grands equally. Part of the enjoyment of the zones and especially with the new additions of terrain is the openness and ability to fight ANY member without having to be invited to a special in-game rank only.
Another good example is Gyururu. She is a Jounin as many know and I'm proud to say someone who could very equally take me on, a Grand hokage.
And for my last example, there are some ongoing RP's between some members and the <Neo> clan and those RP's will start to become limited with the 'level-only' areas because there are people there from EVERY rank involved.
Please revert this back to its original state, this Sannin-level, Hokage-level zone areas are just a bad idea and will decrease Roleplaying more than increase it.