I will not be going but a few people I work with are planning their trip. I told them I would ask around. I know it is a bit late notice but plenty of people have said you could still likely book a room in several places in Vegas. So I am looking for suggestions for the best places for them to stay. They will be in Vegas from the 22nd until the 26th.
I was looking around and it looks like the ARIA hotel does a lot for Christmas. I can't say as far as availability but maybe they'll be able to find something.
I have never stayed in Vegas for Christmas so I can't really make any personal suggestions. I can look up some reviews for you and see what I can find if you'd like though. I know a lot of people on reddit go during Christmas so you might be able to find some good suggestions reading through their board. I wouldn't bother asking as they can be pretty rude.
Planet Hollywood is always my go to but I would also say Aria is nice also.