We always go Christmas week. We were just there 12/20-12/29.
Here is what you can plan on.
Starting the Saturday before Christmas the parks will all have very extended hours. For example -
*The MK will have EMH hours every morning starting at 7am.
*The MK will stay open until at least 11pm every night. Some days it will stay open until 1am. With EMH 1am - 3am. I know it is crazy.
* At the MK they always run two parades a night. There will be an earlier parade, wishes, and another parade. The second parade is always less crowded.
* Epcot future world is always open until 9:30pm with WS open until 11pm. They do have EMH that extends that also.
* AK is usually open until 8pm - EMH extend that.
Basically they park hours are very extended. What I would suggest if you are dying to plan now. Pick where you want to do, plan it, and get a hopper pass. Hopper passes are great Christmas week because of the large crowds. If one park is packed - hop to another.
We love Christmas - it is amazing. Go to the parks at rope drop, leave around noon and hit the pool and relax, go back for dinner and evening in the parks. Pre book all your FP+ for the evenings when the lines are huge. FP+ worked GREAT for us a few weeks ago. We loved having them planned and changing them when needed.