If policing was done to enforce one carryon, boarding would be accomplished a lot quicker and there would be room for everyone's bag.
Took a DL E175 from LGA to DCA on Saturday past: Guy sitting next to me had
1 rollaboard
1 backpack the size that you use when hiking - i.e. a large one
1 regular size back pack.
1 he placed over him
1 he placed behind our row
1 he placed in the overhead across from us