Solo players never face a premade
A player who queues alone for a battleground in World of Warcraft: Forever will never face a premade. Premade groups are only matched against other premades. Blizzard said it in episode 4 of its podcast, which is all about PvP.
Friends who play together in a small group do not have to fear a full premade either. Senior Game Designer Josh Greenfield, known as Aggrend, says there will be a small-group option. Such a group will probably hold two or three players, but that number is not final.
Battleground matchmaking changed once before in WoW Classic. In Phase 2 of Season of Discovery, Blizzard made it less likely that a premade met a group of random players. After some time in the queue, those rules no longer applied. Whether Forever drops the rule after a long wait as well, is not known.
The rest of the PvP plans from the podcast, from less Honor in Alterac Valley to war games, are in our post about episode 4.
Source: Wowhead