The old saying "Anything Can Happen In The WWF/E" is actually the first thing that popped to mind when I read that Lesnar ended the streak. Vince used to say that a lot when he did commentary back in the day, and it never rang truer than when Lesnar broke the streak last Sunday. Then again, there's been a few things that have happened in the last few years that were once thought to be largely improbable (albeit none as shocking as the streak ending at the hands of Brock) - The Rock becoming WWE Champion again, Brock Lesnar returning, an Indy darling like CM Punk getting a long reign with the strap and getting to feud with the likes of Rock and Brock Lesnar, etc. And, of course, the fact that if you had said eight to ten years ago that Bryan Danielson would one day become WWE's most popular star and win the WWE Championship in the main event of Wrestlemania (the same Wrestlemania where the streak would end), you would have been laughed out of the room.
I've read a lot of people say that it restores their faith that Cena will not only turn heel one day after all, but that it could happen sooner than we all think (I don't mind Cena as a babyface personally, but it is something to think about...)