Cena/Rock II is ruins the "Once in a Lifetime" promotion they've used for their first match. Obviously Cena would win, but really who would care?
Rock winning the title is pointless unless he sticks around for a few months, defends it, and drops it someone on his way out.
Rock vs Lesnar doesn't interest me too much considering A) Rock's wrestling ability isn't what it was 10 years ago, B) When the match ends, both will be gone and it does nothing for the company in the long-term.
Rock vs Undertaker - they never had a good match when both were in their prime, so I can't imagine them having one now. And as said with Rock/Lesnar, when it's over, they'll be gone. Rock back to Hollywood, Taker out on his hiatus.
Cena vs Undertaker is the only one that interests me because there's a sliver of a chance they'll let Cena end the streak. But it's a sliver of a chance.