It looks like the moonkin community has decided that the Tier 8 set bonuses are likely not worth giving up the tier 7 bonuses for. In his blog, Graylow has spelled out the math for the 2-piece bonus and decided that the effect needed to be doubled to be worthwhile. However, it’s possible that doubling the amount of damage done by Eclipse may not be a good choice for a set bonus effect.
Why is there a problem? Well, the tier 7 bonuses buffed insect swarm by 10% (2-piece), and gave a flat 5% crit all the time (4-piece).
Why would moonkin want to trade that for a small buff to Eclipse (a random proc on a 30 second cooldown that sometimes gets wasted), and for a random chance for starfire to be instant-cast? Why would we want to trade bonuses that effected us all the time for bonuses that only sometimes buff stuff?
Moonkin DPS tends to be spiky and random because we don’t have control over Eclipse. Some good or bad Eclipse strings can have a huge effect on our damage done, making the T8 2-piece bonus more risk than reward. The only real skill required is managing the buffs and debuffs.
So, maybe the T8 set bonus needs to be something less random. If it makes the devs feel better, I promise that moonkin in PVE will keep using eclipse even if the T8 bonus doesn’t buff eclipse.