Don't like Blue Mage? Here is how to convince SE to change it...

[Fyce]

Define what? It's pretty self explanatory..

"A new and unique way of interacting with old content" is a sales pitch. Nobody wants to interact with old content, that's why it's dead, that's why it needs a sales pitch. If everything else about BLU was the same, except it could be leveled to cap and participate in all the content, this "new and unique interaction" would be the same, no? The unique interaction with old content is not exclusive to this version of BLU. Any version of BLU would (ideally) provide it. The absolute only thing that's new and unique is the Masked Carnival, but again, this is not something exclusive to this version of BLU. They could've easily made the Masked Carnival for BLU regardless of which version of BLU they were working on.

Like the person you were replying to, I have no interest in Eureka, I have not even accepted the first quest. It doesn't matter how many other people find it fun, it doesn't sound fun to me, it doesn't sound enjoyable. So I don't do it. I get the same impression for this version of BLU, equally grindy and, until SE says otherwise, ultimately as useless.

Why does it matter that the content is old if it can provide a new experience? Every content will become "old" after you clear it once anyway, but that's not to say that it becomes worthless, especially if we get a new take on it. Why do you think they made the "New Game+" feature that people have been requesting for years? The very point of this feature is to redo old content (solo MSQ instances in particular). According to you, that's "dead" content. So what is your explanation as to why are people asking for it?
Old content is not worthless. Old content isn't bad. Old content isn't useless. If you only want to do new stuff without having to step a single toe into stuff you've already done, even if they provide a new experience, that's all fine and dandy but then MMORPGs are probably not the thing you're looking for, as recycling content is one of their primary way of keeping people busy (for obvious reasons).

What's relevant is not the age of the content, it's the experience it can provide. And saying that Limited BLU won't provide any new experience is dumb, especially while this implies that non-limited BLU would.

Finally, if you think that the Masked Carnival could be made for a "regular BLU" instead of a Limited one, you've pretty much missed everything relevant to the point of even making BLU a limited job in the first place, as well as the Masked Carnival specificities themselves.

interacting with old content is irrelevant if the old content doesn't change at all.

FFXIV is a MMORPG. Recycling content (without changing it) by making new ways of interacting with it is their bread and butter. Why the heck are you playing this game if you value the novelty of the content more than the experience it can provide? You are literally playing the worst game genre for what you showed as your taste.
Edit:

Halatali is barely alright, i pray to get more interesting things like HW/SB leveling dungeons

At least I didn't get you wrong. Your primary critera for ranking content definitly seems to be its age and not the experience it provides. Which doesn't make sense in a MMORPG as they do the exact opposite (ie: creating a low amount of new content (mostly through the same pipeline) while trying to keep the old one relevant).