Somewhere I read, or misread, that a variable can be a member of multiple namelist groups already. If that’s not the case, it was not my intent to propose it here. Maybe that’s what @sblionel meant by “multiple concepts you’re trying to shoehorn”.
Yes, you can do so already. However, the Fortran language likes verbosity, which is often very helpful for compiler optimizations but also, in many cases, unnecessary. Currently, one must list the variables separately for each namelist group.