If someone wants to use "default" relays they can use it (tab in relays settings).
Discussion
No one uses the default relays. So, that's not a good assumption. In the current implementation, they can change all relays at will, but if they don't have a nip50 compliant relay in the list, the app adds one to make sure things work. Breaking seacrh-related features wouldn't be good. Again, I am happy to explore other models.