I'm weighting several possibilities. As there *is* already an armor mechanics in the game, I'd rather make use of it than add another layer of damage mitigation on top.
I don't rule out a block% yet, but my current plan is:
currently: armor subtracts from 33%-100% armor.
future, without shield: subtract 20% - 100% armor
future, with shield: subtract 40%-100% armor.
certain skills will increase that 40% when using a shield.
If you have armor 20, example.
2h warrior subtracts 4-20 from blows.
shield warrior subtracts 8-20 from blows.
(add to that the stats of the shield itself, and it'll likely be around 9-22)
with this, the effect will scale up as you level, which is the current problem with shields.
disclaimer: actual values subject to change, I am still computing stats and simulations)