Everyone always needs productive wide attackers (except City basically) and the market will create movement.
Chelsea could well be replacing Hazard, Barca replacing Coutinho, PSG might finally sell Cavani or Neymar and if Mbappe is up top, RW is free. Madrid seem likely to get rid of Bale, so a Sancho-9-Asensio frontline makes a ton of sense. Bayern probably can't get him but need him the most. Atletico Madrid too, though they probably can't afford it.
Players move centrally as they get older too, so while Barca play a 4-3-3 still, they're been moving to a 4-4-2 with Messi more central and Dembele as a winger. Sancho on the opposite wing would be devastating. Similarly, Juve buying Sancho to hit crosses at Ronaldo and paying for it by selling Dybala would make sense. Would you want to play Juve with Cristiano as a 9 and Costa and Sancho providing him chances?
I'd say United, Chelsea and PSG end up bidding hard after Hazard finally leaves and PSG sell one of their front 3.
He's 18. Barring serious injury, he can be sold in 5-10 years for at least his value and basically just cost wages, even if he ends up being a top 30-40 player and not a Ballon d'or winger.