I doubt they WWE wants to end the streak
I think what you mean to say, is you doubt "you" would want the streak to end. The W.W.E., on the other hand, could care less. They want whats in the best interest of their company, and if seeing a streak ended will help them, they'll do it.
Now, the key to that, is finding the right guy to do it. Randy Orton and his "Legend Killer" gimmick truly should've did it at Wrestlemania 21. Edge is the next logical choice, because they have to find someone it can both help, and make sense to give it to. Edge has overcome several odds, however he still needs that "one little thing" that will make him forever remembered, as one of the greats.
Edge`s title reign is very unpopular while The Undertaker`s streak is far too popular
Again, "you" think this, not W.W.E. "I" for one love Edge's Championship reign, because I'm an Edge fan. Millions of people all over the world, who both like and dislike Edge, LOVE his Championship reign, because hes a great talent.
therefore if they end The Undertaker`s streak the rating on all brands will severely plummet.
How on earth do you figure the ratings on all three brands would plummet. #1, explain to me how E.C.W.'s ratings would either rise or fall due to something that doesn't effect them at all. #2, explain how Raw's ratings would rise or fall when both guys involved are Smackdown wrestlers.. and finally..
Explain to me, how people won't tune in to see A.) How Edge defeated Undertaker.. when noone else has been able to. and B.) Where this will lead, because obviously whomever defeats Taker on the Wrestlemania stage.. Taker will in turn make their life a living hell, in trying to get revenge.