It looks like a new grenade will be coming to Fortnite Battle Royale, called the Shockwave Grenade. It looks like this will be a legendary Impulse Grenade and according to some data-miners, will be the item that is released next week. If this grenade is in fact legendary, it will be the first grenade introduced that is of that rarity. The Smoke Grenades are of epic rarity, Impulse Grenades are Rare and the normal Grenades are common.
As with all new items that are added, Epic will update the in-game news feed, atleast a day before release, to announce what will be coming.
Epic have not officially announce anything yet and so it is not confirmed this will definitely be coming next week, but we will keep you updated with the latest.