There really is no neutral authoritative source of information on your questions. Oil manufacturers want to sell more oil. Filter manufacturers want to sell more filters. Car manufacturers hope to avoid giving away new engines on warranty. Advice givers (us) don’t want to urge our best customers to take any unnecessary risks with their engines. So even if it were indeed true that you could safely go 30,000 miles between synthetic oil changes, who in his right mind would urge you to do so?
In short, we just don’t know. Considering what’s at sake it is surely best to play it safe.