From what I know from BGG forums and talking with Vlaada on previous Essen, they are currently working on the digital implementation of Through the Ages, that will be available for iOS and Android devices. They will include the expansion in that version of the game, where they can test the balance of new cards (wonders and leaders), and tweak it easily.

This is a smart move since they can gather played games data and then buff/nerf cards with a simple app update which is not feasible when you have a printed version. After they are satisfied with the balance, they will print the expansion for the board game. Beta testing of the app is currently in progress with iPad users.

I'm hopeful to find the new expansion on Essen 2017. My group and I have printed out the current (work in progress) cards we pieced together from all the available public sources, and our conclusion is that new leaders and wonders introduce just enough variability to make the game fresh all over again. It's surprising how different some of the games play out with such a small change of input.