Remove unaltered chunks (was: Convert world as part of update)

As much as I love the version updates, v1.13 has greatly increased the frustration level of having large worlds that can't take part in the additions without traveling thousands of blocks generate new chunks that will take advantage of the changes. 

Granted, I have a very limited knowledge of how the world files work, but it seems that if Mojang would add a routine to remove individual blocks that have not been altered, the existing world would regenerate all the new biome changes. 

Couldn't this simply be part of an update; at least one of this magnitude?