We're going to be living with concurrent ArcMap and ArcPro projects for many years. It would be good to have best practice or at least suggested folder structure(s) for projects that want or need to use both of these products at the same time on the same data and maps. What have you tried already, and from that experience what works and what doesn't?
Keep in mind there's never going to be a realized ideal. Meaning: please don't turn into a litany of complaint thread. Both products have deep assumptions about folder structure that can't be easily changed. Recognizing that starting point, what practical things can we do to make using the two together somewhat more efficient and productive?
(That said, please do feel free to link to other places, Ideas for instance, where those itchy things have potential for change.)