I've been looking through the new Physics Overflow beta¹ and looking back at some of the discussion about the closure of the Theoretical Physics SE. From a purely personal perspective I would prefer research level questions to be asked here because though it's very unlikely I could answer any it's interesting to see other peoples answers. However I appreciate that active physicists don't want to wade through acres of basic questions from non-physicists.
At the same time there are lots of non-physicists interested in physics as shown by the proliferation of science programmes on TV, and I believe strongly that there should be a site for anyone interested in physics to get clear and authoritative answers to questions at this level. I think Stack Exchange is the best place for such a site because it's designed to reduce the junk and advocacy that swamps other less regulated fora.
The approach taken by the Theoretical Physics SE, and now the Physics Overflow, is to split off the most advanced questions, but history shows you end up with a site with very low traffic. I wonder if it would be better to split off the low level questions.
In my perfect world that would leave the Physics SE at a higher level and hopefully manage to both attract back the higher level users and keep the traffic high enough to keep the site vibrant. The Popular Physics SE would provide interested bystanders with their answers, and maybe it could take a more lenient attitude to homework.
My perfect world doesn't exist, of course, and there are obvious problems such as how to decide which site to post questions on. My suggestion would be to use Physics SE for undergraduate and above level questions and Popular Physics for everything below this. I note the blurb for the Physics SE still says Physics Stack Exchange is a question and answer site for active researchers, academics and students (my emphasis). Assuming we treat the sites as siblings, migration between them (mostly from Physics to Popular Physics I'd guess) would be less of a big deal than attempting migration to unrelated sites like the Math SE.
I think that's about it - I will be very interested to hear other views on the idea.
¹ Note that the Physics Overflow is not part of the Stack Exchange network