The fact that barbarian-paladin is normally an impossible mix led me to my initial decision to drop it from the book entirely.
I don't generally like the idea of including really off-the-wall stuff in the series. I would be most happy if DM's felt that they could trust the stuff coming in from my books without having to stretch a lot of rules or make odd concessions for the players.
But, there was enough interest in the Bbn-Pal to convince me to find a way to include it. In the end I decided it really wasn't my business to worry about the character's backstory and trying to explain his class change and dramatic alignment shift.
The end result will be, as many of you have guessed, something along the lines of the Harrier or Blackguard-- a little of both. The class requirements are a little more difficult to fix to encourage a barbarian-turned-paladin, but it's doable-- though of course really it's doable by any class combo, you just delay things if you don't have the optimum class mix.
A straight paladin can do it fairly easy too, which suits the concept as well. In fact I think the class will be most appealing to the fallen paladin. One little slip-up, one act of rage, really shouldn't end your career, not a half-orc, after all; and if Torm, Tyr, or Heironeous can't cut a fellow a little slack, there are others who will...
The Bbn-Pal WILL ride forth...
Wulf