Why wait? Because the developers at Repos want to take every second that they can to test and retest the design, to look at every icon on every card and ensure that it all works together. I recall talking with Thomas Provoost about 7 Wonders: Cities when that expansion was in development, and he would explain why the effect on this card was changed in response to such-and-such an effect on a card from the Leaders expansion and this card's cost was changed due to the B side of one of the wonders and so on. Bauza relayed similar stories at Gen Con, with the Repos team continually testing (as shown in the tweet below), Provoost calling him up to explain why something needed tweaking, etc.
Playtesting, again, with the @ReposProduction team ! with @BDMontagnes #7wonders Duel pic.twitter.com/TuBeNghwLj
— Antoine Bauza (@Toinito) June 3, 2015
So while the details of the game itself were still being finalized at Gen Con 2015 — meaning, the game hadn't yet been sent to the printer — the nature of the gameplay is clear, and Cathala and Bauza spent a few minutes presenting an overview of the game, which I described after a test game at Origins 2015 as "75% 7W w/ the 25% new stuff being ideal for the 2p game". Yes, 7 Wonders for two will become a reality in just a couple of months...