The announcement for September and early October updates informed players of a massive update coming to Duel Links. This update is scheduled to happen mid-September and is speculated to be adding 5D's World similar to how GX World was added in a "massive update" late last year.
The soundtrack for YuGiOh 5D's was played during the WCS 2018. This could be a way Konami is trying to hint at the release of the third generation of YuGiOh in Duel Links. If this is true, it could be similar to how YuGiOh GX was confirmed for Duel Links during the WCS 2017 tournament.
What is yu-Gi-Oh 5D's
The third generation of the Yu-Gi-Oh series. This generation saw the introduction of Synchro monsters which was the first ever mechanic that expanded the extra deck beyond Fusion monsters. This Generation also prominently featured the Turbo Duel format, meaning we might get Turbo Duels in a future event.
Synchro monsters are identified by the white color of their cards. They are placed in the extra deck sharing space with Fusion monsters and other future extra deck mechanics. This means you would have to manage your extra deck better to fit everything you need. But also means that you do not lose consistency when running them as they would not be drawn from the main deck. The general rule when Synchro summoning a monster is sending 1 Tuner monster and 1 or more non-Tuner monsters to the graveyard whose total levels are equal to the level of the Synchro monster you would like to summon. Sometimes there are additional specifications to this rule, like only using a certain type of monster as material, but these will be specified in the card text. Synchro summons are also a type of special summon.
The Protagonist of the 5D's series Yusei's deck contains lots of protection effects and support for his ace monster. Helping him keep monsters on the field long enough for him to Synchro summon into his more powerful monsters. His ace monster is Stardust Dragon which offers great protection from destruction effects.
Jack Atlas is Yusei's rival and is reflected by the kinds of cards he uses. Converse from Yusei's defensive Strategy, Jack uses a lot of high-attack monsters and power cards to destroy and inflict damage to his opponent. His ace monster Red Dragon Archfiend is able to destroy all your oppenent's defense position monsters with just a single attack.
Akiza is a Signer with power psychic abilities. She uses a Plant-type deck focused on control and summoning her ace monster Black Rose Dragon. Black Rose Dragon is a powerful monster capable of clearing the board and also a secondary effect to change a defense position monster to attack position and reducing it's stat to 0.
A good friend of Yusei, Crow uses a Blackwing deck. Blackwings are one of the most beloved Archetype in the series with their ability to spam the field by Special summoning and Synchro summoning Blackwing monsters. Even with relatively low attack stats Blackwings offer a variety of powerful effects that compliment each other. Crow's ace monster could either be his original Blackwing - Armor Master or his Signer card Black-Winged Dragon.
Leo uses a Morphtronic deck whose play style revolves changing their battle positions to gain effects that fit the situation. His signature monster is Power Tool Dragon that can search your deck for Equip cards which can then be used to power himself up and gives him a layer of protection.
One of Yusei's old friends that came under the influence of the Dark Signers. He uses his Infernity deck with his handless strategy to make use of his monster's effects that mostly focus on the graveyard. His possible ace monsters are Hundred Eyes Dragon, Infernity Doom Dragon, or his Dark Signer ace Earthbound Immortal Ccapac Apu.
Carly uses a Fortune Lady deck that is able to manipulate it's own level through effects. Their level also increases every turn and their stats increase with their level. Her Signature monster could be Fortune Lady Earth or her Dark Signer ace Earthbound Immortal Aslla piscu
GX is extremely lacking in the girls department, there's literally only one other relevant girl in the series: Blair Flannigan, whose "Mystic" cards are not only incomplete, but also not printed in real life.