How nothing has changed
Eclipse was given a huge makeover in Cataclysm, so to say that nothing has really changed feels a touch misleading; however, I assure you that the statement is fairly accurate. To explain, here is how the new Eclipse system currently works. Balance druids get a new UI bar under their name plate that contains a sun and a moon which fills up with a different color, shifting from one end to the other, depending on which type of spell damage you use; there is also a numerical display on the bar to show exactly how many Eclipse points that you currently have. Once the bar reaches one end of the spectrum, which occurs at 200 points, you then gain a buff to your nature or arcane damage for 15 seconds.
Sounds awesome, right? It isn't.
There are two core issues that we face with Eclipse today: It accounts for far too much of our damage, and we are double-penalized by any movement that we have to do while Eclipse is up. For all intents and purposes, this is still true for the Eclipse of tomorrow.
The damage portion of Eclipse has been reduced to only a 20% increase (in the current built at least; this is subject to change). However, this damage increase also scales with the mastery stat that is found on gear. For those of you who have good memories, this is still a higher increase than the original Eclipse had back during the Wrath beta; back then, it started out at 15%, then was eventually increased to 30% for Starfire. Even with all of the other damage modifiers that we currently have and that any player has, a 20% bonus is still a very significant deal, the reality being that it is much higher than any other increase that we currently get from our other talents. With Wrath of Cenarius no longer affecting Starfire and Wrath, the only competition that Eclipse has in terms of damage is Starlight Wrath, Vengeance and Nature's Grace, which really isn't much of a competition at all. Only Vengeance should have close to the same impact on DPS that Eclipse currently does.
This is problematic because it means that, once again, Eclipse is going to account for far too much of our damage contribution, to the point where we are forced to have as high of an uptime on the effect as we possibly can (although, to be fair, this is going to be true no matter what the damage modifier is). That, my friends, is one of the largest issues that currently afflicts Eclipse; balance druids will always, always be balanced around the notion that we get as many Eclipse procs as possible within any given time frame. The current bar system allows for some control over when we choose to proc Eclipse -- at least more control than we have now. Yet control isn't something that we particularly needed; it removes the annoying RNG factors associated with Eclipse, which is a quality of life improvement, but it doesn't address any of the fundamental flaws. The control is but a mask for the fact that we will still always want to proc Eclipse as frequently as we can due to the fact that the damage increase is simply that significant. Further, how much of the proc that you can utilize right at that particular moment is generally of little consequence; delaying a proc now also delays a proc later.
Movement, on the other hand, is a completely different animal. Note that I wasn't implying before that the capacity to control is a terrible thing -- it's great, to be honest -- just that it doesn't really hold any sway over how we deal with Eclipse. The impact that movement has on damage is all merely a function of Eclipse itself; the more damage that Eclipse accounts for, the more it is penalized by movement. The interesting thing at this point is how Eclipse is going to scale. At 20%, Eclipse still will account for a significant portion of our damage. But it still isn't the 40% buff that we know today, so while movement is still a major factor, it isn't as terrible as we currently see it.
However, most of this is really left in the unknown, depending on how badly movement will end up impacting our DPS and Eclipse itself. Many of our talents have changes, so while Eclipse itself may have been nerfed, so too were other abilities in comparison. Further, Blizzard has been taking strides to make caster damage while mobile a tad bit higher -- not exceptionally high, but better than it is now. For balance druids, I can say that this end of the experiment isn't going too well; that is, however, a different topic for another time. Even still, Eclipse is half of the reason why movement will always hurt us far more than just the simple DPS difference between Moonfire and our other abilities.