The biggest issue is with the current balance changes as reported is that currently lunar shower is (1) useless, actually harmful to have in PVE and (2) still promotes an activity Blizzard does not want us to do in PVP. So basically in an attempt to nerf the ability in PVP, they turned lunar shower into a talent only PVP boomkins will take.
Let me elaborate.
In PVE, Lunar Shower has had two uses. One, and I believe it is the primarily intended purpose, is to give you a nuke that you can use while you are on the move. Like other similar moves (scorch, aspect of the run, etc) it gives you less damage than your standard rotation but still allows you to do something. Now even in its current iteration it is somewhat weird in that at times you have to make the choice of either not using it or overwriting a superior dot on the target (for example you have a sunfire up, but moved away from eclipse when you suddenly have to change positions). In this regard, the new lunar shower is significantly worse than what we have now: basically if you elect to use it in an eclipse state when you have to move (once again: this is why the talent is there in the first place) you are going to waste eclipse energy from your more damaging attacks -- and if you are not in an eclipse, you will suddenly overwrite your superior dot. Basically, with this change, lunar shower becomes useless for the very thing it was created.
The other (probably side?) effect lunar shower has was to increase our AOE dps in multi-dotting scenarios. I believe that blizzard changed the nature of the lunar shower nerf to still enable us to multi-dot in a PVE setting, thereby leaving our AOE capabilities only slightly nerfed. The problem here is that the FIRST stack of lunar shower appears during the first sunfire and stays there for 3 seconds, and an IS-SF cycle is shorter than 3 seconds, so you will still end up cannibalizing your precious eclipse energy -- that is, unless you do not take the talent in the first place.
To sum it up, in PVE it does not serve as the "use when move" skill it was meant to be, and is actually detrimental to our AOE ability -- becoming that mandatory talent to SKIP. That can hardly be the intention of this nerf, and also carries the side effect that our only "mana saving" ability has to go for better performance.
In pvp, if you still elect to play as a boomkin, you will still have to rely on this ability as one of the very few things boomkins can do (as explained here: http://eu.battle.net/wow/en/forum/topic/2123512981).
There are other ways to curtail sunfire spamming. I believe one of the easiest solution would be is to make the initial damage portion of both spells to be not affected by mastery. Doing this would ensure that the ability would not hurt our AOE rotation and still find some use in single-target pve (at least in soloing/questing or in other mana conservation uses; the overriding of a more powerful buff would still be an issue), while the current reforge-everything-to-mastery pvp "builds" would suddenly notice a 70%+ nerf to their damage, ensuring that sunfire spam would not be so "overpowered".
Mind you, even this change would do little to help the current abysmal state of boomkin PVP, but on that front we can just hope. Hey, at one point they promised us instant starsurges with knockdown, and instant root that could be talented to affect multiple targets. As we have seen and read from the frost mages, instant aoe roots are not overpowered, just make your healer dispel (remember the arguments about the cat nerf?) The knockdown component to an instant starsurge would serve as a good way to give us breathing room against both melee and casters -- and hey, I would HAPPILY give up the current proc-based "burst" mechanic associated with the spell, and instead accept our role as a capable CC character. Anything better than the current feathery punching bags with cramped fingers.