This means nothing. She got new dancers after the first 2 years as well. They probably sign 2 year contracts along side Britney's. I'm sure after 4 years some of the dancers want some more flexibility.
It'll be extended again and they'll just get new dancers.
But if it's true then YEEEES. Good, do a WW tour Britney. You're in the best shape of your life, this is the best dancing you've done in the past 12 years, and you haven't toured worldwide since 2011, it's been 6 damn years. All of these reasons alone will make the tour do better numbers than the Femme Fatale Tour.