The Battlefield 1 Premium Pass includes four expansions—They Shall Not Pass, which was released to all players yesterday (Premium Pass holders got a two-week head start), and the upcoming In the Name of the Tsar, Turning Tides, and Apocalypse—each of which includes a number of new multiplayer maps. That can lead to problems when people who have the pass (and the maps they contain) want to play online with their buddies who don't.
EA's solution, as announced today, is Premium Friends. Simply put, it means that as long as at least one person in a multiplayer party has the Premium Pass, all other players will be able to play on those new maps, regardless of whether or not they own them.
There are a few restrictions: Only owners of the pass, or the relevant individual expansion, will earn experience from playing on the maps that are exclusive to that expansion, although earned experience for non-owners will be banked and granted retroactively if they buy it. Non-owners also won't be able to spawn with weapons and vehicles that are unique to the expansion map they're playing on, nor will they be able to make progress toward expansion-specific medals and codices.
By all appearances it's very similar to Doom's PartyPlay system. From EA's perspective it's all positives: they get props for throwing out a freebie (though many players still argue DLC maps should be entirely free), premium maps are more fully populated, and players see what they're missing—and maybe have second thoughts about throwing some money at it. A "test run" of Battlefield 1 Premium Friends will begin March 30—as in, tomorrow—during the next Battlefest.