They’ve stated in some cases conte t will be fine on old worlds and where possible they will try to keep that the case. However new content might i my spawn in unexplored regions of old worlds.
So if you’ve not found most lands yet (the next biome release) you might just wish to hold off that so you can have a better chance of spawning new content.
The next major update is speculated for August which will be Hearth and home and has more recipes, new building materials and pieces, and new flaura.