Thinking about the ramifications of Mexico's possibly winning two U17 World Cups in six years, I looked at the 13 previous winners of the tournament, which was first held in 1985. You do see some correlation between U17 success and trophies for the adult teams: Brazil has won three tourneys, been runner up twice, and lost in the semis twice. Spain also has a pair of runner-up finishes, and two more semifinal losses.
However, Nigeria has won three titles and lost three times in the finals, and Ghana also had a pair of titles in the 1990s. Switzerland is the defending titlist. Even Saudi Arabia has a title. And the list of undistinguished semifinalists is really quite extraordinary considering the relatively short life of the tournament: Bahrain, Qatar, Oman, Burkina Faso, and Guinea have all made it to the penultimate round. In general, South America outside of Brazil and Europe as a whole are very underrepresented: the only titlists from the latter continent are the Swiss, France in 2001, and the USSR in 1987, while Uruguay is the first non-Brazilian finalist to ever hail from South America. So, in summary, good for Mexico if they can pull off the title in front of their fans, but glory in Russia 2018 is no foregone conclusion.