Legally, a room has to have a closet and a window in order to be called a bedroom. The best sleep I've ever had was in what's known as a "non-conforming" bedroom. It was a basement addition that had no windows. When the door was shut and the light was off, it was completely dark. Insulated by the ground, there was almost no noise, either. It was wonderful. I miss that little non-bedroom.
I love the summers here in Oregon, but I don't love that the sun is out for so much of the time that I'd like to be sleeping. The light wakes me up, or makes it hard for me to sleep restfully, and I know I'm not the only one. Good luck getting your toddlers to go to bed at a reasonable hour in the summertime, too. "But the sun is still out!" As much as I loved my windowless room, I doubt it's a trend that will catch on. The next best thing is a good blackout curtain.
I got these inexpensive Deconovo curtains on Amazon, and I'm very happy with them. They're attractive and effective — almost as good as having no bedroom window at all 🙂