I don't eat a ketosis type diet personally and don't have any experience with it as far as knowing someone personally who uses it. I understand that some use it to cut weight before a show, which apparently it is good for. I don't believe it is necessary to use over an extended time frame.
My diet averages around 50-60% carbs, which mostly come from vegetables, fruit, wild rice, millet, quinoa, and amaranth. I seldom eat potatoes, bread, pasta, white rice, cereal, etc. I think oats are fine, but they give me indigestion. So while I am not on a low carb ketosis type diet, I am still careful about where my carbs come from, especially the complex carbs I consume.
As far as eating simple sugars before bed, in theory what you suggest makes sense as far as causing an insulin spike and possible weight gain but I have never experienced that as a problem. For someone who wasn't very active or was eating candy/soda type simple sugars it could be an issue. If I eat before going to bed it is usually a fruit smoothie or nuts/seeds and usually 1-2 hrs before actually going to sleep. I usually only do this when I have a late workout and I then get hungry after the workout, so similar to a recovery type meal.