LordEntrails
Hero
Good question.I take your point, but I'm thinking of it from the perspective of "how much stuff ought I write"? If there are, like, enough enemies in the 'early' sections that the party could earn enough XP to reach 10th level, that makes later sections perhaps-boring cakewalks.
I suppose it's feasible to cater to multiple playstyles, perhaps with sidebars highlighting how each section could be trimmed down if the GM only wants X encounters. Or rather, it would probably be easier to build a functional spine, then give 'greebles' (a term from Star Wars - little doodads they would glue onto ship models to make them look from a distance like they had realistic textures appropriate for huge vessels), by which I mean a selection of bonus material that the GM could decide to use or not without messing up the broader geography and flow of the dungeon.
To me, the difference between a very large dungeon (LD) and mega dungeon (MD) is a MD is simply too big to ever complete. Taking a completionist approach with a MD just doesn't work. There's too much there for a single campaign or set of characters to ever do, or need to do. Sure, maybe the first few levels/areas are completely explored, but after that kicking in every door is just... boring. And that then it becomes goal or objective oriented. IMO its a lot like a traditional campaign setting. A single campaign is never going to explore every part of Greyhawk or the Realms, etc, but rather bits and pieces of it. i.e. the party might spend some time in Waterdeep, and then in Luskan, and maybe a few adventures in the Dessarin Valley. But never will they fully explore each and every one of those.