Hi Scott, hope you continue to be safe and well. I agree, the Rock is not coming back, Cena cannot wrestle anymore as he even stated he does not have one more match in him. That is why he opted into the cinematic match with the Fiend. I honestly see Big E. winning the Rumble and challenging Reigns as the safest option. Another option could be Daniel Bryan winning the Rumble or the Elimination Chamber and then having to go through the Uso's to get to Roman.
The wildest option would be CM Punk, he's not 50, but, from a storyline perspective it makes sense. The shield debuted by saving Punk. The history between Punk and Heyman. Also, Roman can keep the silence and let Heyman and Punk do the talking.
Let’s just let the dream of CM Punk die in peace. And remember, it can always be Sheamus.