Today Airbus did their yearly press conference to review the past year. The media does get over-hyped days before it and writes about the "order battle" between Airbus and Boeing and speculates about who won the "order race" - as if it would matter if one or the other got a few more orders than the other. For years now the number of orders are close at the end of the year, showing that there is some kind of natural balance in the civil aircraft duopoly. If there were not a balance, there would not be a duopoly.
That brings us to the future, there were will be no more a duopoly: Bombardier will be the first to break into the territory with the CSeries - I still believe we will see one or two orders until the BBD financial year ends at January 31.
Then the next one could be Embraer, if they decide to build an aircraft similar in size to the CSeries - or probably a little bit larger to undercut seat mile costs.
The chinese will take a little bit longer to make a difference, I think. Even if they would be able to bring their C919 to market in 2016 - and I doubt that - it would be limited either in numbers, as initial production numbers will be low in comparison to the A320(NEO) and B737 and geographically as I do not think that western operators will take that aircraft until reliability is proven and an acceptable maintenance network is in place.
The russian MS-21 will face the same problems - EIS in 2016 is an amitious goal and Irkut will have to work hard to sell aircraft outside the russian area of influence. I wonder to whom the first firm customer, Crecom Burj, a new leasing company in Indonesia, will lease their 50 aircraft. Reportedly they want to serve the whole southeast asia market...
So at least in the narrowbody segment there is an end of the duopoly in sight. For the widebody sector the end is far further out. One day the chinese will do a C929 or C939 or whatever it will be called, but I would expect they will go through a second round with their C919 first, trying to make it really competitive to the (then) established products from Airbus, Boeing, Bombardier and Embraer.