If a new guy hadn't beaten the Streak, then I can think of one guy who it would have been fitting to do it- KANE!
I know that UT-Kane has been done at both WM14 and WMXXX, but they had Austin-Rock three times.
Kane would have been more suitable, since he was a character based around the Undertaker's origins. Being his storyline brother, and one of his greatest opponents, it made sense. Also, it would have made sense for Kane to don the mask again.
Maybe Undertaker should have come on Raw pre-WMXXX, and confronted Corporate Kane, and chastised him for what he has become- no longer the "Devil's favourite Demon", but a man wearing a suit- Triple H's bitch. Undertaker should ask where the Kane he used to fight was? This should anger Kane, and force him into donning the mask and going on the warpath. He would then defeat the Undertaker at WM, which would bring a fitting ending to the UT-Kane feud once and for all, and then it would give Kane more credibility in his feud with DB over the WWE Title (as Bryan has to beat the guy who ended the Streak to keep his title, making the threat bigger). But all having Brock Lesnar do it achieves is giving Heyman bragging rights.
For me, I would have had someone like Kane or Bray Wyatt do it, or have had HBK do it as WM26, and keep his career going.
Historically maybe, but Kane is nowhere near credible anymore. He's not even a favourite to beat Daniel Bryan how can he ever be considered legit to end the streak? I've always loved the Kane character but his threat is long gone since his constant chopping and changing of character.
I get the anger about a part-timer ending he streak, but fact is whenever Brock turns up he's over, he gets heat and he draws. He doesn't need to be there every week and anything he could've done immediately after WM would've been pointless as he has just ended the streak, how can it be possible for anyone to beat him so soon? They need to build the Reigns and Cesaro's of the world up to be at a level for when Brock returns for us to go "hang on, maybe he can beat Lesnar." And right there is the rub those guys need.
Because so soon after WM, there is nobody on the roster I'd be convinced right now could beat Lesnar. What him ending the streak achieved was creating the most dominant wrestler on the roster and the most over heel to be called on at any time to benefit the younger guys.