I was looking at some of the combat logs, and all of the bonecrushers and blademasters out there seem to be using two weapons at the same time. What would the viability of a blademaster/bonecrusher using one weapon and a shield at the cost of the extra attack to be able to use the shielding skills from knighthood and combat?

The extra defence afforded by wielding a shield is nullified when compared to the fact that with two weapons, you do double the damage. No real BM/BC fighter uses a shield consistently with a single weapon, though they usually have one handy to shieldstun.

It's not worth it.
Maybe warriors will get some weapon/shield style one day...

Why? All a shield buys is more physical protection and as a warrior you'll:

* be more likely to be a race with high con and high str rather than mage/guardians who generally have to pick high int races with appropriate low con;
* be able to wear better armour than anyone else in the game

So why use a shield as a knight for anything other than stunning?

Actually daevos use to use a shield/broadsword.. shieldstun then swing. stops healing

I use sword/shield when I spar weaker guild members to help them train.