DICE has finally provided the roadmap for Battlefield V through Fall 2019. Included in this roadmap are mentions of new maps, which look to begin in May, and a new theater of war. Given the name of the new theater, Awakening the Giant, slated for Fall 2019, is the upcoming theater of war.

Given the title of that new theater, I think it's safe to say that they're referencing the United States. This is based off of the famous quote from Japanese Admiral Isoroku Yamamoto in reference to the United States following the attack on Pearl Harbor by Japan.

I fear all we have done is to awaken a sleeping giant and fill him with a terrible resolve.
If there's no weirdness going on from DICE, I think it's safe to say that the new theater of war will focus on the conflicts between the United States and Japan. Get ready for Wake Island Part 5: The Wakening!

Truth be told, there's nothing concrete about the new theater just yet. DICE did mention, via Reddit, that they're "not blind to the conversation" about making sure there are a bunch of maps ready to go for the new theater's release this Fall. However, if you want new maps, the Fall isn't going to be your first opportunity to get some. The first new map since the game's release is actually going to be released this May.

The new map is called "Mercury" and it takes place in the Mediterranean, specifically on the Greek island of Crete.

We're cranking up the intensity even further later in Chapter 3. During this time, you’ll experience unexplored fronts as the fight moves to Mediterranean – with the addition of the Mercury map. Here, you'll take on a massive aerial invasion along the Cretan coast and experience the first and largest German paratrooper invasion ever, based on the real-life events of Operation Mercury.

There’s also another new game mode coming. In June, you’ll secure and build objectives to ensure your team assembles enough soldiers to endure through the fight. This is the premise behind Outpost, and you'll find more info about this multiplayer experience and further Chapter 3: Trial by Fire details on the Chapter 3 page.
Another map, releasing around June, is called Marita and it also takes place in Greece. The latest roadmap gives a good idea on when you'll see the new maps and other new content. For more details in the form of written word, be sure to hit up the latest official Battlefield news post about this roadmap over at the Battlefield website.

Battlefield 5 2019 roadmap