What are the limits on baking at 400F/200C?
That temp will cook many, many things with no problems. You would simply have to adjust cooking time.  Also, regarding your article and video, many Thanksgiving items are simply casseroles that need to be heated through (other than the turkey), so one temperature makes sense.  Speaking more broadly, oven temperatures are wildly inaccurate.  So, a setting of 400F is often meaningless, unless you are carefully monitoring your temperature with an oven thermometer placed inside. It would be fairly common for your oven temperature to be significantly (as much as 50 F or more) different from your oven setting. If you have the time and energy, an oven set at 400F could cook things that need a much lower temperature, provided you shuffle your items in and out of the oven with the correct timing. Perhaps not so convenient, if you needed to set a custard in a water bath at a low temperature.  You may also be limited in cooking that requires very high heat.  For example, while you could bake an edible Neapolitan pizza, on a stone, in a 400F oven, you would simply get a better result in an 550 degree oven (and in less time).  So, practically speaking, I think the bottom line is that, with the exception of some specialty items, the limits here are mostly time and convenience, rather than temperature.  You could eat well using an oven that only had a 400F setting. I would say 475 - 500F would be less practical, but then again, if you only had one setting, you would adjust your cooking to the heat source.