The game was intended to go to level 10. They figured out that they need a few levels more. I don't think that it will go to 20. I think helping Jergal to take back his power from the three would be interesting.
Since I'm pretty sure Jergal likes to hang around my campsite and occasionally revive my fallen companions, this seems quite possible.
Also, I'm hoping the game or its DLCs, or at the very least its eventual sequel, will allow us to go to level 20+ because I personally really enjoy playing with massively overpowered characters against super high level enemies. It's spectacular, epic, and a whole lot of fun.
