People have been saying it won't be long until more cores are needed since time began. More cores simply aren't needed. Four cores for the most part are complete overkill.On the other hand it was only a short while ago people were saying an i5 is your best bet for gaming. That quickly moved onto i7. It wont be long before 6 cores are needed. Whether its zen or zen+ nobody knows but its something to bear in mind.
Don't forget we are a very niche section of an industry which simply doesn't need to cater for us. Just check the most popular gaming rigs on steam and you'll see a desktop i3 is even way too much!
I would consider those who max a cpu during gaming i.e those who lower settings to get 120+ fps to be even more of a smaller segment of the market. Even the GPU vendors are getting this now having reduced sli/cf support.
Quite simply by the time more cores becomes a necessity zen or at least the first generation of zen will be long past it.