One of classic IA arguments is about why New Service X shouldn’t be added to the primary site navigation.
Users aren’t *generally* just wandering around the internet going “ooh, what’s that? I have no idea, why don’t I click it and see”. If you just add random new stuff to the primary navigation, the main thing that will happen is it will get ignored as users carry on their journeys to wherever they were already going.
It can work ok for a new product category e.g. groceries but it really isn’t very effective for a new brand or unfamiliar feature e.g. X-PIL. Combined with a big marketing push it might work, so you can get away with it if you have reason to believe this is going to be a really big new feature e.g. iPlayer *and* you are going to heavily marketing the brand.