I think he could be a big star, it all depends on how you use him. In fact, I might get some WTF's? for this but I think that if you wanted to continue to use The Undertaker gimmick after The Undertaker himself leaves, you could have this guy take it over and continue the legacy of that character. You could have this whole angle with Taker where his body is breaking down and will not be able to continue on as the vessel for the spirit of The Undertaker, he could announce this as a prelude to his retirement and this would be his last program. Andy Levine could come out as his "Silent Rage" character and tell Taker that he is the one to continue the legacy of The Undertaker, to Takers disbelief.
This would result in Undertaker putting him through a series of matches against other opponents where "Silent Rage" would have to prove to Taker that he is indeed the one to become the new Undertaker. At some point Taker begins to take more interest and see more promise in Andy as he begins to become his protege. As the relationship develops, at some point Andy comes back to remind Taker that his whole intention was to replace him as The Undertaker and that he hasn't forgot why: because his body is weakening and can't continue it for much longer.
You could carry this on for months if you want, 5 ppv's in a row leading up to a final showdown at one of the big 4 where Andy would then face The Undertaker himself in the final test: a casket match. If Andy wins he becomes the new Undertaker, proving that the current Undertaker truly has been broken down and can no longer carry the spirit of The Undertaker. If Andy loses, The Undertaker proves to still be the one and walks off into the sunset, never to allow one to take his rightful role as The Deadman, as The Undertaker.