He is definitely a Ni-dom, and I can see aspects of Fi that soften his Te-ness as well.
He is hard-core rationalistic, but lives in a world of possibilities and can process speculation in a rationalistic manner. He seems introverted because of his reserve and his focus on ideas. It is harder for people sometimes to see what Ni looks like because it isn't as external as Ne. I would say Carl Sagan provides the opportunity for people to glimpse inside a deeply Ni thought process.