Can gluten-free flour be cooked and eaten as a hot breakfast cereal? I'm talking about single flours, such as quinoa flour, amaranth flour, and buckwheat flour, not flour blends or hot cereal mixes.
Yes, you can do it. It will taste more like a pudding (not necessarily wheat pudding) than like a cereal. The consistency will depend on the grind size, and can get down to standard starch pudding, or be a bit gritty like semolina pudding. 

Most people won't find the taste of a pure flour + water or even flour + milk pudding interesting enough, so you can experiment adding stuff to it. You're only limited by your own imagination.