#4 Shinsuke Nakamura
If there is a talent currently under-pushed in WWE who could truly become a main-event player in any other promotion, it would be Shinsuke Nakamura.
He did receive a coveted Royal Rumble win last year, as well as several WWE Championship matches with AJ Styles in 2018 but nothing came from the matches and Nakamura was then thrust into the mid-card. He did win the US Championship but had a mostly forgettable run.
He's currently looking to reclaim the title from Rusev at the Royal Rumble, but with the likelihood of retaining the belt looking slim, he might start to become bored.
Companies like Ring of Honor, New Japan Pro Wrestling and All Elite Wrestling would be backing up trucks of money in order to sign the international star.
If WWE lets him slip through the cracks of their roster, they might just see Nakamura departing after his three years with the company.