Update 1.6 introduces the Soviety MiG line. You can sit in the cockpit of Yak-inspired MiG-3 in tier V, and going all the way through to tier X with the high-flying MiG-15bis.
There are also new Premium planes which you can buy and fly. From the far-eastern Chinese P-51K, to the sky-storming U.S. XP-75 Eagle
What's more? There are new class of multirole aircraft
And also interface improvements and map extensions.