EX content locked until:
day 3 = minehole lv2
day 7 = minehole lv3, snekkjas, steel
day 14 = minehole lv4, knarrs
day 21 = minehole lv5
day 28 = minehole lv6, trolls, bone clay
day 35 = minehole lv7, cave conch
day 42 = minehole lv8, orcas
day 49 = minehole lv9, realms, whales
(semi-random times as an example, whales/orcs/minehole levels being the important ones)
The quality/industry grind for haven is very front-loaded. If you know what you're doing you skip 99% of the content, but it's still so much work that it encourages /a lot/ of people to play together or make alliances just for industry purposes.
Spreading the content out similar to example above would make it more reasonable to play at a competitive level without turbo autism rushing certain things - which would make the early game more enjoyable, make more people competitive in industry, and provide less benefits to being in a big zerg.
https://www.wowhead.com/guides/wow-clas ... ent-phases
https://elysium-project.org/timeline
Classic WOW is kinda like haven in that it was originally intended to be something you play forever, but ended up being basically seasonal for 80% of the player-base. Almost every(literally every?) successful private server has progressive content where more end game stuff is locked for a good while.
I've personally played through vanilla wow ~5 times, and it's a lot more fun to do content in a somewhat intended order as opposed to ignoring MC to do Naxx trash in greens. The equivalent to which in haven is spending 90% of your early game killing whales with a Q13 spear and collecting wax for mineholes while force feeding one guy so he can mine level 9 with a Q100 pickaxe <2 weeks after server up.