The only real answer is that no one knows for sure.

New items like onions may not have spawn points generated in places you have already been and exposed the map already.

New build parts in menus should not be an issue unless they use some new resource.

Personally I develop a seed to a certain point I am happy with it and start a new seed and repeat. This way I don't "over explore" my only world, and have plenty of worlds to choose from when they do add stuff to expand with.