The kids stayed in the tent for about three weeks this summer. They had a grand time and had big plans to stay out there forever but we had to pull the plug due to too much Alaskan-summer-funitis... (translation: it is impossible to sleep when the sun doesn't go down for long!) I'm sure we'll have more deck tent adventures in the future but I might wait until September when the quality of sleep can improve a bit due to more dark sky time.
Oddly enough when I google blackout tents I don't see a huge number of them. I do see all sorts of hacks that desperate sleep deprived families camping with babies or toddlers try, but not entire tents. I think there is an untapped market available!