Were you replying to someone or was that just completely random?
I too doubt it that he will get 500 wickets, I have high doubts. But you never know. If he gets enough Tests, and NZ attack doesn't perform, he bowls lots and lots of overs injury free, plays for a long enough time (I reckon he could have a maximum of 7 years left, but I think it'll be more like 3-5 with his workload), then it could be possible.