Quote from ezfe
I don't think you guys get what he's saying
lets say your seed is "123" You hash that and get something like 202cb962ac59075b964b07152d234b70. You then use this to generate the world
A simple mod could be made to remove this restriction. Also, 3rd party tools for mapping and stuff based on the seed would still be able to generate the correct map as they would not alter the entered seed.