There's certainly no reason a Leadership mechanic like 5e couldn't show up in a future 6we book.
But as is.. Leadership is a suggested specialization of Influence. What Leadership does as of now is apply +2 skill ranks to your Influence skill test in whatever circumstances the GM agrees "Leadership" is a sensible fit for. As FJ noted, it does exactly the same thing as Negotiation.
Personally, I never thought 5e needed both the Teamwork rules AND the Leadership rules. And of the two, I thought Leadership was the one that was less necessary. Because let's face it... all Leadership did was allow you to do a Teamwork test with someone without needing to know the skill yourself.