Opening up the off-hand slot for THF, I think is a wonderful idea. It removes item grind as a consideration in balance, and makes the whole system much easier to manipulate.

The B of S&B should be made to have equivalent demand to other items in any solution, for obvious reasons. Having a unique item in the off-hand slot for each style allows the devs to focus the benefits to the role. To be honest, I think defining that role for S&B, (which is currently 'laughing stock'), will be the hardest bit about balancing.