Sure, and even ideas that have been written about can be more precise and complete, perhaps by writing more about them, for example, so no one has fully formed ideas by this logic.
Depends on the idea. To me the whole article was too generic or handwavy without giving specific examples of what kind of ideas are actually fully formed and which are not.
What is a definition of an idea that is fully formed and that is sufficiently complex enough?
But also, if more writing can always make the idea “more complete,” then no one at all (even the people who write) has any “completely complete” ideas.