Honestly, even if that match was ever slated to happen(after Cena became their top guy), I'm not sure Cena would have even agreed to go over. Taker was the first guy that congratulated him after his debut. The conscience of the wrestling industry, who at that time was also the Undisputed champion and the biggest heel in the company, praises your first match. Taker basically broke character to give Cena his endorsement. When have we ever seen him do that? You can't get higher praise. John Cena has too much respect for The Undertaker and I seriously doubt he would've agreed to beat him, especially if it was for the Streak.