I'm going to be adding a better form input to highly recommended users to use good passwords. Since it doesn't store the master password (just the key derived

I'm going to be adding a better form input to highly recommended users to use good passwords. Since it doesn't store the master password (just the key derived from it), that is the true "game over" but would require trying the whole 2^256 space with HMAC-SHA256 to brute force the key. If they try to brute force the actual mastet password, it would be extremely slow since it uses scrypt with a high n, which runs at 2 hash/sec on a good desktop (probably could be a lot higher using dedicated hardware, but still very very low compared to SHA256 which stands at millions of hash/sec). I don't understand your last point, can you rephrase it?