Global Categories

This may be a feature request but am wondering if it is possible to set up the categories on the sites so that there is a standard. On Etsy you have to select one of the given categories or maybe have an 'other' option.

Am thinking the global category list could get pretty long. Also when I list the global categories will it list duplicates if two sites have the same category.

Maybe I am just not sure how it all works. I just know on the sample site I set up, my main site categories did not show and I could create my own.