An intelligent user can create seed himself or add any of words and symbols as entropy.
You can and should not ever rely on the user to be the source of entropy, they will never create strong ones ever.Quote
As an option, I will add the ability to use any arbitrary file as a seed, and multiple hash (>100000) to slow down brute-force, this will be really reliable, I believe. 
This makes your program to be a brainwallet which are very unsafe and 100k hashes does not make brute forcing slow.