I think people are afraid Rusev's undefeated streak goes to Cena, a guy who doesn't need it. But there's no doubt the match(es) will be very good-great.
Right... I think everyone wants a Cena-Rusev program... that makes Rusev stronger.
Totally true, but this idea that every unbeaten streak needs to be broken by some up and comer who "needs it" is flawed. If that happened every time it'd be predictable. Underdogs can't win in that scenario every time, then they wouldn't be underdogs. Sometimes the monster heel who's unbeaten needs to get beat by the top dog. But just not their first match.
I think we all figured that Rusev was being built up to be fed to Cena. I think what you're hearing is the combined scream of "No, not yet!"