Definitive is a name to me as much as HD is one. It’s not a state.
I don’t expect AOE4 being more popular than AOE2, especially with Relic’s latest track records and the fact that AOE4 just seems like an AOE2 rehash. AOE4 development has anyway nothing to do with the one of AOE2, because those are two different game dev teams.
By the way, somebody found three campaign folders in the game data. They probably won’t launch with the November update but I kinda expect them to be launched next year, might it be through free updates or DLC. Maybe those are for new civs, which would be awesome.
Source: ETA of the November patch?