Serious question: Why bother developing for hardcore players in any capacity? Why bother continuing the stigma of MMOs being for "no life neckbeards"?
Why? Raiding is boring as fuck. Come on, we've done this shit for almost 2 decades now. It's the same formula every time. Clear some boring trash packs, wipe on a boss a bunch of times, then everyone miraculously learns the encounter during a random pull and you down it. This is repeated ad nauseum. Why center an entire genre around this singular experience?
Someone needs to make an entirely casual MMO. You can have something take a while to obtain, but you can design it in a way that there's no real benefit to doing it as fast or hard as possible. Most MMOs these days are just funneling EVERYTHING into raiding. Everything other than raiding is there to get you closer to raiding.
Instead of straight up vertical upgrades and progression, reduce the exponential rates of progression and introduce horizontal progression as a side thing. Dungeons are a fine replacement in lieu of no raids in an MMO. Make the dungeon crawling experience immersive, eventful, and even hard for some. You should be able to do challenging content without feeling like you need to invest yourself into an MMO big time. Without feeling like you need to devote dozens of hours a week to it. It's lame.
There are plenty of features to introduce into an MMO to make it fun for a while without needing raiding. Deep crafting systems. Deep, customizable housing system. Fishing boats, merchant boats, naval vessels designed for combat. Realm vs. Realm PvP. Duels. Merchant systems where you actually feel like you're building a business empire. City systems where you defend your town and populace from invaders, these kinds of things. Garrison invasions? That shit could be 100x cooler.
If I was making an MMO, I wouldn't even bother trying to get the crowd that rushes through my content and completes it all in under a couple weeks then is anxious for more. No one needs those players, they are an extreme minority. And they are cancerous to good game design.
Look at the bullshit that happened with Everquest and Legacy of Steel or whatever it was called (Kaplan's guild), why deal with that bullshit at all?