Well, you'll actually be able to use another on it the next turn, although I'm not sure if there should be something to stop a chain of them just continuing as long as you have another shield bash... ex: I just used a shield bash. 1 turn till my shield is destroyed. I just used shield bash, another 1 turn till my shield is destroyed.
Nah, i don't believe chaining should be allowed :/
I don't think it'd make sense in the code.
So I would sacrifice my shield for a maximum of 16 damage? I'm not sure that's favorable. Perhaps don't make it twice the damage, just make it a regular amount of damage, and your shield isn't destroyed.
The number of times you can use shield bash is the number of times you can use it within the two turns from the first shield bash to when the shield is destroyed.
So, 6 shield bashes in hand + 6 quanta of any time + upped hope = 96 damage in one turn.
Of course, you either need epic stalling, fast draws, or both.