Something tells me this year will be 2015 all over again, which was the first year with no new main series release since 2011 (yes I know that was the year Black/White came out, but only outside of Japan) as far as I recall.
I feel that we may be going from a new main series entry every year, to rather being every two years, and that means generations may be getting shorter, since 6th Gen lasted pretty much the same amount of time as 5th Gen, in that both had only two main series releases. 7th Gen might follow this pattern once again, with another 3-year generation.
Going by this logic, we probably may have to wait until 2018 for a new main series game at the earliest.