That's a cute idea. Let them hit "Next" and then surprise attack with it, giving them a "Wait! I didn't write down my seed, go back" option
Discussion
There certainly is something to be said about "shock value" x)
I like the idea of training a user to write down their seed. It is less painful to fix the didn’t write down my seed problem at the beginning rather than after they generate content.
You could explain to them that they will be prompted to re-enter their seed value, and you can also explain to them that they can generate another seed at any time but will lose control of their content at that time.