i think that this will be a good idea but what i think we should do is keep the old map but when a new update comes all u have to do is keep walking some where new and the chunks will load the new stuff.
and we should move the spawn to the the stuff.
p.s:will help with the new spawn if needed
"Old worlds will not get errors, but you will need a new world to get jungles" - Jeb
The new biome will not load in new chunks, without using NBT.