Regarding Ashe's passive, my 2 cents.

My idea to her passive would work out like this: Her passive would stack up to 100% bonus damage while she doesn't attack, so waiting for the last hits would be little to no problem, and that % Bonus Damage would be consumed on her next AA after activating her Q, so, in this system, we'd keep her gaining stacks over time like the live passive and solve the problem of wasting crits on minions or being rewarded for not accomplishing the DPS position that's expected from her, and maybe last hits could add +1% to the count, rewarding good players in the last hit mechanics, answers appreciated and replies will be listened, sorry for any wrong spelling, English is not my native language.

Tl;DR: Ashe's passive crits only proc on her first AA after Q is activated.