As I mentioned in my previous post, I believe (and it has been rumored) that the 60th anniversary celebration and related events will last all year and carry into the first part of next year, and then stop somewhere by spring, or before May 2016. The 50th anniversary celebration carried over from 2005 into 2006.
In other words, more than likely, the new events of the 60th will be going on in some capacity throughout the whole year -- which is why it could impact crowds throughout the whole year and into next year.
I doubt that Disney would spend money on a brand new nighttime parade, new fireworks, new whatever else, and probably some random pop-up events here and there, then only run them during the summer and that's it. The schedule might change a bit -- the events could go from running nightly to a more limited schedule in the fall, but I think that they will still be going on all year.
In 2005, the holiday fireworks were shelved so that Disney could run other fireworks in celebration of the 50th anniversary.
So what I am saying is that I suspect something similar will happen this year -- the holiday season entertainment is probably what will be impacted in some way by the events of the 60th, not the other way around. I don't know if both the Christmas parade and holiday fireworks will be removed from the roster completely in 2015, or maybe just one will be removed and not the other one, or if they will be reduced to some sort of hard ticket Christmas party situation, or just scaled back to a limited schedule, but I think that the events of the 60th will take center stage from May on through the end of the year and into next year.