We've done it (in 2015) and will never do it again. I agree with the PP's. Get to the parks as early as possible. Avoid MK on Christmas day (at the very least. If I ever did it again I wouldn't go to MK at all that week). When doing EP, avoid WS during CP show times OR, if you plan on going to CP, get a dining package. Book dessert parties or dining packages (when available) if viewing any nighttime entertainment. Do EP FW during CP shows (it's much less crowded). Don't go to DS. Do things off the beaten path. Go to a park in the morning and go to HDDR, SOA, do a monorail tour, head to the Boardwalk, visit Ft. W and take a sleigh ride etc. at night. Use your resort amenities (pools, pool parties, movies at night, etc.). Book a tour (if they are offered and available). We did Wild Africa Trek and it was perfect that week because it got us out of the AK crowds. Pre-book FP+ (I would probably book them starting around 10 am). When making ADR's, make them in restaurants close to where you will be (ALL transportation will be difficult that week).
We survived the week and managed to have fun, but, I can't emphasize enough how crowded MK will be that entire week.