Heya Heraclius! Currently it is not known how we will earn our reputation for the Queen's Wrath after September 8th. Bungie has yet to comment on this matter. But! In theory you can still reach Rank 3 before the update. You can earn Queen's Wrath reputation by completing Wolf Pack Patrol events and opening the Ether Chest found in the region. Be warned though, the rep earned there is mediocre (if I recall corrently, +18 with the Nightfall buff).