#3 Could be champion by the end of 2019: Samoa Joe

Back in 2005, Joe was asked if he would someday work for WWE. Joe's response was classic Samoa Joe all the way; "When hell freezes over."
Joe wasn't actually opposed to the idea of working for WWE, he just figured he would never be on their radar because of his natural build, and the fact that most of his mystique revolves around his legit bad ass character and stiff and brutal wrestling style.
Breaking Vince Russo and Jim Cornette update HERE.
However, never say never, because Joe did end up signing with WWE. He was perhaps the biggest name to come through NXT at the time, an international Superstar and former world champion of multiple promotions. After becoming the first ever two-time NXT champion, he was elevated to the main roster.
Why he might be champion before the end of 2019: Joe has become a stalwart performer and reliable mic man for WWE. He pretty much has all the tools he needs to perform as the champion.