Would Luffy wear a crown ... no. A bangle, a skull, a viking helmet, mask, robot head .... sure. In the literal sense there probably is no treasure to have a crown with. The literal treasure is most likely the truth of the void century, and after learning how the world is and was, I belive Rogers left it all in one piece, undisturbed. Rogers was the king for going the farthest, but kept going until he got sick. Whitebeard probably was closest to a figurative crown if he had tried harder. Rogers was crowned for exploring the farthest, Whitebeard was crowned for having the biggest alliance. They both achieved their goals. Luffy will get both, as I think he will unwittingly have the most flags and support come when he needs it, than anyone in history. That will only happen once he declares war a second time. BB or nobles he is going to rock the world. Crowned a world legend and then at the end probably take off his hat at one piece which is probably a massive grave/shrine to an unspeakable tragedy.