Very good question. Idealistically, a system should be as revealing as whatever the microphones pick up. Or at the very least, whatever musical info has been stamped on the disc.
However, the problem lies in the fact that almost every system we ever hear fails miserably in one or more of the numerous categories that make up the musical presentation of what one might consider a musical, tonally rich, warm, blooming, full, robust, detailed, transparent, open and airy, dynamic, and involving musical experience.
Therefore, simply making a system more revealing(which already exhibits one or more serious shortcomings), tips the scales that much further in same direction for which the system has already set it's course. That is when the ear starts to bleed or when the listener starts to wince at certain passages.
Some to many inherently know when something should sound real but instead sounds more like fingernails on a chalkboard. And when we start to hear passages that come across more like fingernails on a chalkboard and we know it shouldn't sound that way is exactly when listener fatigue sets in.
On the other hand, when a system is extremely well-balanced from the top to bottom most octave, a system can never be too revealing. At this level of system, only the very, very worst recordings are intolerable. But then again, they always were.
Additionally, with this same well-balanced system all the other so called poor or mediocre recordings (which are many) that on most systems sound rather lifeless, flat, and 2-dimensional, will instead sound nearly as tonally rich, 3-dimensional, bloomy, warm, full, robust, detailed, transparent, open and airy, dynamic, and involving as your favorite reference level recordings.
So I suppose the answer to your question is two-fold:
1. For those whose systems are significantly lacking in one or more major categories, it simply will not take much to become too revealing. It easily becomes too much of a good thing.
2. For those whose systems are well-balanced and maintained as such, there is no such thing as too revealing and therefore, there is no end in sight as every upgrade in the right direction is considered a major sonic upgrade with benefits typically across the frequency spectrum. Thus maintaining that balance.
Of course, personal preference is such that for some, a system is always deemed to be too revealing.
Many times it's because they've been told that true high-fidelity is meant to sound soft, veiled, etc..
But other times the foundations of their system configuration is already out of whack but are forever dealing with the affects rather than the cause.
-IMO