I think not. In trailer of AoE IV, narrator said: “Now, a new age is upon us.” I believe this AoE IV will cover I and II World War. Even Main developers - Relic, is known from games from that period.
But, this is just my opinion.
That ad was purely speculative and has been dismissed by developers. It is absolutely not proof that sequels will continue to advance into the 20th and 21st Century. They were just messing around.
Bear in mind that there already was a sequel to AoE3. It was Age of Empires Online and returned back to classical antiquity. The next game in line was Age of Empires Castle Siege, which runs up to the Renaissance.
If this franchise is ever going to breach into tanks and planes, it will be totally unprecedented and bizarre.