How Nature's Torrent interacts with Eclipse is obviously the larger picture here, and sadly, we don't have any information about it at all. All that we know is that this function of the spell is what really matters. How Nature's Torrent works with Eclipse is going to make or break the fun factor of our cast sequence.
There are almost limitless possibilities as for how Nature's Torrent could interact with Eclipse. To start with, the spell could function as an "execute" ability of sorts, where it gains a very large damage bonus from wherever you are on the Eclipse spectrum but shifts you completely to neutral or perhaps even towards the opposite effect. For this to work, druids would probably try to get their Eclipse bars shifted as far to a single side as possible before unloading a powerful burst attack. Then the process repeats itself. In this function, the damage of Nature's Torrent is paramount, while the actual utility of the spell is rather superfluous.
A similar method would be that it doesn't totally shift the scale but does impact it significantly for higher amounts of damage. Say, for example, that you are fully Solar. At this point, you could begin the 1221221 or whatever sequence of rotating Starfires and Wraths to maintain that level, or you could use Nature's Torrent for a larger burst of damage at a higher cost in shifting the scale -- say, down to halfway between full Solar and neutral. Once you hit the apex, this would cause the rotation to be NT > Wrath until full again > Starfire if NT on cooldown > Wrath back to full > NT. Although it would still be a set rotation of sorts, the rotation would deviate based upon haste and crit values, with higher haste allowing for more spell casts before the cooldown on Nature's Torrent is up again and crit increasing the rate of Eclipse gain.
This is but one theory, and there are many, many others out there currently. Nature's Torrent could act as a form of the new Steady Shot and increase our Eclipse gain/consumption for a period of time. Perhaps Nature's Torrent will be just a massive shift in Eclipse, and you try to keep your Eclipse values balanced towards neutral until you can use it. Or perhaps Nature's Torrent will become Eclipse as we know it today, at least to a certain extent, meaning that when you cast Nature's Torrent, it locks in the Eclipse buff you currently have at the expense of shifting you to the neutral zone or merely being unable to shift the scale back towards that direction for a time.
There are far too many methods in which Nature's Torrent could possibly function with Eclipse. We have no solid information to go on, nothing at all -- yet as I said, speculation is good. Just don't allow yourself to get too hung up on a particular version of how Eclipse and/or Nature's Torrent will function. If the new revision of Eclipse tells us anything, it's that Blizzard really knows how to hit into left field.
Eclipse and scaling
Finally we move into the last aspect of Eclipse: how it is going to scale. Scaling is a very fickle issue in this game, and balance druids are certainly very keen on it. We've suffered through various scaling issues at differing points of the game that have hindered our ability to perform. How Eclipse actually works with all of the stats that we get may not hold a major impact on the fun portion of the bonus, but it will certain influence our DPS capabilities. As with everything else, we know very little of how Eclipse is going to scale; we do know, however, that there are going to be two key scaling components that need to be looked into.
First and foremost is how Eclipse is going to scale with haste and crit. Balance druids currently have a love/hate relationship with both of these stats to an infuriating degree. We want and don't want both at the same time. It's a hurtful, abusive relationship that needs to end. I tend to think that Eclipse is probably going to exist similar to a system that mirrors rage. For those who don't play a warrior, rage functions off of a pretty basic formula; the warrior hits something and gains rage based upon the damage that he deals. Critical hits grant more rage, and the faster he can swing due to haste, the faster he can generate rage. If you do follow warriors, then you also know that rage is being normalized in Cataclysm once again, so that it no longer is a function based on damage done but merely a function based on hitting the target. For example, a normal swing grants 5 rage and a critical hit grants 8 rage. The main reasoning for using such a system is balance. It is very easy to tweak and balance around a variable standard of resource gain than it is to balance around completely random resource gain. Ghostcrawler (lead systems designer) didn't outright support this system, but he did hint towards it.
Ghostcrawler is correct that a flat system wherein each spell gives a set amount of "Eclipse points" based upon a normalized formula can lead to a rather boring rotation that doesn't have much flow to it. That being said, we've also seen with the current rage system that basing such things on damage done can be quite a difficult task. Although it would be slightly easier to accomplish with spellcasting and the removal of incoming damage altering resource generation, it would still be very difficult to tune it to a level where it is perfectly balanced across multiple gearing levels. In this case, I say that simple is probably best. A simple system where each spell moved the Eclipse bar by a specific amount normalized, or not, around base cast time while critical hits give adjust the bar slightly more is going to be the optimal choice. This would allow for nominal amounts of scaling by both haste and crit while not having to factor in the scaling of spell power and proc effects, which can cause hiccups within the system. How each of the stats would or should scale is up in the air, as would how we would end up favoring each stat under such a system. It is still the best possible choice for achieving overall spec balance.
Last but not least is the scaling form the mastery stat itself. We know that mastery is going to be a new stat that appears on higher-end gear and that we are all going to want this stat, but how it interacts with Eclipse specifically is a bit of a toss-up. It hasn't been laid out in blue text yet, but it is a sure guess that the mastery stat will more likely than not increase the damage modifier attached to Eclipse. It is possible that mastery could increase the rate at which our spells alter the Eclipse bar instead. Either system seems like it is going to end up being a bit awkward -- not so much in how it effects our ability to deal damage or in how we are able to model it, but more so in how Blizzard will express it in game terms.
There's a hefty wait-and-see aspect in all of this, which is basically the mantra of any Cataclysm discussion at this point. All of that notwithstanding, balance druids still have some solid ground to stand on. Eclipse is changing. How it's changing, we know; if the change will function the way Blizzard intends, we are still pretty clueless. The only answers can be found in more information that isn't going to come out until beta does. In the meantime, speculate away. It does wonders for the soul.
Every week, Shifting Perspectives treks across Azeroth in pursuit of truth, beauty and insight concerning the druid class. Sometimes it finds the latter, or something good enough for government work. Whether you're a bear, cat, moonkin, tree or stuck in caster form, we've got the skinny on druid changes in patch 3.3, a look at the disappearance of the bear tank, and thoughts on why you should be playing the class (or why not).