Maybe it will be an end game zone in a patch? Maybe its small? Who knows, but they did say that the zones are the biggest they have ever made sooo..
4 Dragonflight zones could be as big as 6 WoD zones or northern or OL. Too soon to see IMO. Pandaria was 5 zones initially and they turned it into 7 due to feedback.
Its also possible that they are going to go smaller scale for the initial expansion so they have dev time for 2 more big zones in patches. 77 day patch cadence with 2 big zones added every 6 months.