This technique shall get nerfed. It is too overpowered and on the same par as a Bijuu. However, if this technique shall get legalized on usage to Shinobi Legends' RP World, then I for one, would say that the Perfect Susanoo should be added/legalized just as much (though, it is nerfed as well). It doesn't really make any sense if this technique is legalized on usage in RP while Perfect Susanoo is not.
Perfect Susanoo would only require 4 Uchiha resets + EMS.
This new Mokuton technique may be pretty powerful, but it requires a total of 10 resets in order to fully utilize it (4 Mokuton, 6 Sage Mode). Sure it may be able to restrain a tailed-beast, but I'm sure a jinchurikki would be smart enough to not go full bijuu transformation, to only get caught in it. They could just remain in their normal state and still have the perks of a truly massive chakra supply.
It seems pretty fair to me, since the Rinnegan can pretty much defy and control some of the laws of life and nature, even at the bare minimum of 2 Uchiha resets, 1 Mokuton reset and 1 Rinnegan reset (4 resets minimum) + EMS.
But we also have to remember that this is a true kage-level battle. So it's not like everyone on the site is going to be able to do all this.