We haven't been for christmas (but hope to one day) but we did do a last minute (2 months out - prior to buying
DVC) NYE trip - I am sure Christmas is much tougher for dining reservations than NYE is but i stalked and stalked and was flexible with where and when we ate -- so we did score something. Maybe some one else can talk about this -- but i am wondering if resort restaurants are any harder or easier reservations to get vs in park restaurants. Might be a fun time to check out some of the other resorts and the decorations. If online right at your 180+10 mark you can probably get something -- might not be what you want but at least secure something then keep looking.
Going at a busy (ok insane) time of is what you make of it -- really set your expectations very low, expect to do your FP rides and use the
MDE app to try to get other rides with more reasonable wait times (under 30 minutes). It is truly magical to see everything decorated for the holidays.