Sometimes I want to open a header that I know is somewhere in the include path but don't know the exact location, and I'd rather not spelunk around in the "File open..." dialog trying to track it down. I'd like to suggest that "Open File in Solution" consider all files that are in the include path when "Show only files in the current solution" is unchecked.
To me this is analogous to "Find Symbol" being able to find symbols even if declaration/definition for the symbol isn't currently 'active' in the current solution when that checkbox is unchecked.
My workaround for this is to type a temporary
#include <whatever.h>
and use the context menu on that line to open the file. I'd prefer not to have to do that, and if VAX can help that would be great!