I love night mode, as I often look at this site before bed. I have a feature on Chrome that allows me to turn the lights off, but I don't think I can really answer questions while it's in that mode. It's more for videos. I think a night mode would be great :)
If that feature was introduced, I'll stop using the mobile version and will use the app only. It will save my battery as well as my eyes :) That would be excellent. I'm glad that this question is featured. It means admins/devs read it.
If you're using an iphone just use tripple click/inverted colours and you dont need the night mode. But for others, it sounds like a great idea. Make it easy to use all the time (on screen/webpages) but not too big that it's annoying