I googled around before typing this and saw how confusing aspect ratio questions/requests can get, so I made some pictures. Hopefully they're more sensible than my mouth-words. You know how sometimes you'll overthink a post and slowly contract many thoughts into a few sentences and they sound kinda goofy? That's what I've done with this.
Oh yeah and it would be nice to be able to choose between nearest and linear scaling, seems like Res Scale is linear.