#6 Shelton Benjamin
WWE Debut: January 2, 2002 (Note: The date reflects his first televised match as part of the “World’s Greatest Tag-Team”; Benjamin had made various house-show and Sunday Night Heat appearances earlier.)
‘Mania Debut: WrestleMania XIX (Triple-threat Tag)
Shelton Benjamin started in WWE as part of "World's Greatest Tag Team" alongside Charlie Haas winning the WWE Tag-Team Championship twice. Quite early in his career, he had everyone believing that he was the next big thing. Since then, he has won the Intercontinental Championship, US Championship, and has had great moments, but Benjamin had never wrestled a singles match on WWE's biggest card.
Moreover, With age not on his side, it's getting unlikely that Benjamin will feature in one. And, that's a shame for one of the most gifted athletes ever in WWE history.
#5 Rhyno
WWE Debut: March 9, 2001 (Note: Rhyno had wrestled in WWF earlier as Gerin in 1995)
‘Mania Debut: WrestleMania XIX Triple-threat Tag match)
The final World Heavyweight Champion of the original ECW promotion, Rhyno, has also never been featured in a WrestleMania singles match. The PWI's #10 'Wrestler of the Year' in 2001 has found moderate success in the WWE. He has won multiple championships and has been over with the audience owing to his beast-like build and his finisher - Gore. Yet, he hasn't ever been overly pushed by Vince McMahon.
While Rhyno has had an entertaining career, we will have to accept that he'd probably never be in a one-on-one contest at 'Mania. Still, he only needs to gore some to steal a WrestleMania moment.