Initially they will have their own "new maps only" playlist, so you guarantee matchmade games on them - then a week-plus later, they will be rolled into other suitable playlists.
Don't worry if you don't have the new maps - the matchmaking won't pair you with games that require them. You won't notice a thing.
As for Forge naysayers - Foundry will for example let you remake a somewhat passable version of Foundation, or even a smaller Hang Em High. It is NOTHING like editing Forge variants on "normal" maps. And remember, a ton of new pbjects have been added for just that purpose - ramps, stairways, imoveable walls and so on.