Fei, I wholeheartedly disagree.
I can't speak to how you feel, or how members of your guild feel about the difficulty of Naxx--but I can tell you how I feel. If we're given an LFR-level-diffuclty Naxx that's cleared by practically every guild on the server within a week, then I'm done. I won't stick around for a second week, and I know I'll be far from the only one. I have too many great memories of the sheer challenge, and feelings of accomplishment that came from clearing retail vanilla Naxx, to tarnish them with the utter disappointment that will inevitably result from an undertuned version.
Perhaps you (and others) haven't realized this yet, but for many people, the only reason they're still playing on Kronos is because they're clinging to this fine thread of hope that Kronos' Naxx is going to be the same kind of epic adventure that they've been reading about since 2006, but were never able to fully experience for themselves. They all know that Kronos' MC, BWL, and AQ are a complete joke in terms of difficulty, but they bite their tongue every week and say nothing, because they think Naxx is going to be completely different, and that difference will be enough to make up for the two full years of LFR raiding, content delays, sever instability, and lack of communication that they've had to endure while waiting. But unless some sort of custom tuning is done, there's not going to be an epic adventure. There's not going to be any sense of accomplishment. We're going to clear the whole raid in 4 hours, and then stop to reflect on the journey: "So that's Naxx huh? Well what a fucking joke. All those people who glorified this place as the hardest and most awesome raid Blizzard ever created are complete morons."
I'll let you guys in on a secret. All those people who glorify Naxx as one of the best raids ever created--well, they were right. It was. Every time my retail guild set foot in there, it felt like we were doing something epic--something special. Every time we killed bosses like Loatheb, Gothik, 4H, Sapphiron, and Kel'thuzad, there was this huge feeling of accomplishment that never diminished after the second kill, or third kill, or the final kill before TBC launched. There was just nothing else like it. And now Kronos has the chance to give our community a similar experience. I don't want to see them blow it.
I'll repeat this again: Challenge --> Sense of accomplishment --> FUN/ENJOYMENT
I don't care if Elysium tried and failed at bringing the hardcore element back to 40 mans. That was AQ, the most hated vanilla raid, and this is Naxx. How many of those Elysium players had already done AQ on Kronos, and were already sick of it after clearing it once over there? How many of their raiders were already spoiled by the lack of challenge on Kronos, and just cba to do a version that required more effort and time? How many players quit, and guilds died due to natural attrition, not difficulty induced attrition? I don't have the answer to those questions, do you?
The bottom line is that Naxx is Kronos' last chance to restore the faith that players once had in it. If Naxx is challenging and memorable, then it'll go a long way toward accomplishing that goal. If Naxx is disappointingly easy, then there might not be enough players left after a few months to justify programming a TBC server. Which would you prefer?