The Undertaker is definitely the next active wrestler to go to the WWE Hall of Fame.
The only problem I have with "classic" wrestlers is that they hang around too long, IMO. I'm not putting the blame solely on them either. I think it has a lot to do with poor choices by WWE talent scouts and management.
They find excellent, jaw-dropping, young talent that will "wow" crowds for years to come, but they don't utilize them properly which leaves them with a filtered, shitty roster to put shows on with. So many younger wrestlers get misutilized and it sucks. Shelton Benjamin, Kenny Dykstra, Chris Masters, etc.
In order to keep people coming to the events and watching them on TV, they almost have to keep the older, "classic" wrestlers around just to do so.