Can I please ask you, OP, and anyone else catering for a special diet this Christmas NOT to make a huge hoo-ha or any kind of fuss whatsoever about it on the day. It may well be new, fresh and fascinating to you, and you may also want to seek a bit of appreciation for your efforts but please, just don't. It will usually be the very last thing the person involved wants.
I say this as a diagnosed Coeliac of over forty years standing. It just reinforces yet again how different you are, and the "othering" and unwanted attention can be deeply upsetting sometimes, especially on special occasions. Sharing food is such a sociable thing for most people, but it isn't for everybody. It can be fraught with worry, stress and even danger for some of us. As others have said, there is also huge social pressure to eat something the host has gone to a lot of trouble to make - (whether you wanted them to or not).
It's lovely that you want to make them feel included, and by all means have a word with them in advance, but please, no pressure, and accept with good grace if they decline your suggestions.
The primary duty of a host is surely to make all their guests feel relaxed and welcome. The special diet person is not there either to polish the host's halo or provide a talking point for their guests, both of which roles I have had inflicted on me in the past. . Please, discourage others from commenting or making a fuss too if you can. It's truly horrible for the person involved, so please don't do anything that might make them feel that way. In fact everybody, can we all just not make remarks about what other people are eating, or how much or how little they're eating? It's rather rude, and I think many of us who have difficulties around food would really appreciate it. 💕