Christmas in the summer

That sounds fun! I would do a July wedding though so it was Christmas in July like PP said. I also think since you said you guys do different things and have a known obsession with Christmas it would be fine. I feel like you could do some fun arrangements!

Personally I LOVE Christmas and have been known to randomly throw on a Christmas carol in July and start buying my gifts in September, but seems like it could be too gimmicky - also Christmas to me (and maybe a number of your guests although obviously I don't know them) is about Christ and I don't like to see it used for gimmicky purposes, so if it was done, for me it'd need to be handled with a respect to the reason for Christmas. Sorry if that sounds prudish but to me Christmas is not so much a "theme" and thinking of it as such gets into cringey territory.
However, if you just love the aesthetic of the season I get that, maybe you could do a "transport to winter wonderland" theme and have lots of evergreens, white glitter, white faux-fur, serve frozen hot chocolate and have cinnamon and peppermint scented everything...ok that could be awesome.