I propose it be put out into the open. Every size penis would be assigned a number or a letter. Every man would wear that letter or number. Could be a button, a t-shirt or even tattooed on their forehead.
A woman could be cruising around and may feel like just giving a blow job. Depending on her preference she could pick an "A", a "B" or whatever. She wants anal she would pick her certain size. Same with getting her pussy pounded. I mean what the fuck. We see the tits and ass, so us guys pretty well know what we are getting into.
But guys are saying, if my dick is what I consider small, everyone will know it. Believe me, long enough with this system in place and it will not really matter anymore. Dick jokes and pecking order would cease to exist. In fact, with it out in the open a lot of pressure and anxiety would be taken off of people as a whole. No more guessing games. No more wondering. People would be free to worry about essential important things.
Hell, there doesn't even have to be a categorical system in place. Everyone could just go naked or wear see through clothing depending on the weather. With that kind of freedom, honesty might be more prevalent and there might be less wars, crime, reality television and so forth.
Does not matter what size your dick is, there will be women interested. The laws of averages, personal preferences, mood swings, and too many other variables would dictate it.