#1 CM Punk
I think CM Punk might be the only one who thinks he still has a career in MMA. If he didn't realize that by his first two outings in the UFC, he might never realize it. Perhaps he likes the challenge, but Dana White said he wouldn't be in the octagon any more.
Punk was teased as being involved with All In, but it never came to fruition. The man himself has said he is done with pro wrestling, but perhaps he just meant that he's done with WWE and big companies like it.
The Elite invited him to join the Bullet Club and his anti-establishment and 'Voice of the Voiceless' mantra would fit right in with all of the antics of the Elite over the years.
Punk was always vocal about not giving a lot of deserving people like Zack Ryder or other mid-card wrestlers the opportunities they deserved and it appears that the Elite are on the same wavelength.
If CM Punk did opt to return to pro wrestling, it would likely be with ROH, NJPW or AEW. He still is a name everyone wants to see return to the ring. Him doing so would be a huge win for AEW and a likely a shot at his former employers.
He is clearly someone who holds grudges, so I cannot see him returning to WWE. Can I see him return to pro wrestling? Since the wrestlers are the bookers, he would likely be more amenable to ideas from fellow performers rather than those in suits.