Its now confirmed 5D’s World will be coming to Duel Links soon.
The “massive update” teased earlier is indeed 5D’s World. There’s still no official date, but said teaser indicated “late September”, so its coming quite soon.
Confirmed characters are Yusei Fudo, Crow Hogan, Akiza Izinksi, Jack Atlas, Luna and Leo for now. The trailer shows off some Synchro Summons and various other cards.