I've been away ever since a month or so after 4.0 launch ... so I've only just got around to experiencing Eureka, and I love it.
I love that it gives me those FFXI feels. I love that monsters will bother to chase me and everything aggros. I love that I got killed by the level 5 Phurble. I love that I lose exp for death. I love that elements mean something. I love that people actually talk to each other and form parties and work together.
I get that not everyone likes it, but I can plainly see that the people in there love it too. Maybe the primary mistake was tying the Geralt quest to it, because that made people feel like they HAD to do it even if they didn't want to...
But there's a ton of other stuff to get, like Materia, Mats, Tomes, Mounts etc (and the joy of just doing it if you're into that sort of thing).
Since it is tied to its own leveling system, it should easily be transferable to future expansions, simply by having it continue to drop both stuff like Mounts, but also current Materia / Mats / Tomes. Stuff that doesn't necessarily force the player to play it unless they want every Mount for completion. But makes it another option, a way to spend time in the game, just an ongoing form of current content by which to progress.
I mean, for me personally, I'll put some time into it here and there no matter what, just because I want to ... but it would seem like such a waste for it to lapse into irrelevance as far as tomes etc. Anyone have a clue about this?