No, it's made clear at Dressrosa. Because he or she won't be acknowledged as the Pirate King by other Pirates or Marines.
For example, Chinjao and others acknowledged Roger as the one who stands at the apex of Pirates.
Sengoku, Admiral at the time, acknowledged Roger as the one who stands atop of other pirates in strength at the time:
Shiki greatly respected Roger's strength:
Shiki, only acknowledged it being Whitebeard's era after Roger passed away, because Whitebeard was viewed as the strongest after Roger.
According to Garp the era between Rocks - Whitebeard was Roger's era, meaning Roger & Roger Pirates reigned supreme on the seas.
ACKNOWLDGEMENT by the world is what makes somebody a Pirate King. Roger' journey to Laughtale cemented his legacy, because he did something that was deemed impossible. The newspapers then labeled him as the Pirate King. Him being the Pirate King was then accepted because it was already his era, he reigned supreme on the seas with his Roger Pirates. The Marines & Other pirates acknowledged him as the top pirate.
Which is why when you have Luffy who gets labled as the 5th emperor, by the newspaper:
No credible person actually acknowledges him as the 5th emperor. Blackbeard even making it clear that he ain't ready for the title of emperor:
Finding the treasure in Usopp's way would simply cement Usopp as a threat to the World Government due to the history there. But he won't be acknowledged as the Pirate King, because he hadn't proven he can stand against the 4 emperors, let alone be above them.
But even if the newspapers say he's the pirate king, the other pirates won't acknowledge him as such like they acknowledged Roger.