Won't be standard legal as they will contain cards from all three ravnika blocks.
September 2, 2018 9:59 a.m.
Hey, to expand on what seshiro_of_the_orochi said. Only the reprints of cards from the previous old Ravnica sets (Deathrite Shaman, Abrupt Decay, Aurelia, the Warleader, Boros Reckoner etc.) will not be Standard legal. Read more about the Guild Kits here.
The full decklists of each of the five Kits haven't been revealed yet, but each Kit is a full 60 card deck. It's very possible that each Kit will contain a combination of cards from the Guilds of Ravnica set, Dominaria set and M19 core set. If cards from these sets are in the Kits than they are Standard legal cards no matter what their set symbol is.