So, it seems like discussion about the Rune of Re-Origination has spiked up a bit lately. I want to remind people of a few things about how stats work together before it goes too far.
1) Increasing one stat increases the value of the others. This causes changes in EP depending on if you add or subtract stats (remember that AP has value beyond "1"). For example, if you have 5k mastery at 1.3 EP, going to 4k mastery could
hypothetically increase that EP to say, 1.45. Similarly, if you add mastery to make it 6k rating, that EP
could perhaps go to 1.2. So taking one EP and subtracting the lost stats from the EP of the gained one is a no-no.
2) Shadowcraft works by averaging the stats from procs. This works well for normal trinkets and procs, but isn't ideal for this specific scenario. The problem is that Rune of Re-Origination dances around secondary stat extremes, losing all of your stat to another causes EP weights to slide drastically, at a rate we don't support well.
3) SimC will struggle to get an accurate modeling of this too. As I said, the trinket dances around extremes, and SimC could support this correctly at some point (I don't know if/when they will get/already got
the negative stat buffs working) but the way the data gets rounded out at the end of their process obfuscates the results without extensive prodding and manipulation.
So the best way to get an idea on how strong this trinket is, is to do all the math with your own stats, relying on your own logs for how mechanics line up with your gear and how often they do. The way trinkets line up, the way phases interrupt flow, you won't be able to get consistent and useful data without getting your hands dirty in some math. This is outside the reach of Shadowcraft as we know it, and maybe even SimC too.
For the most part, you're going to want to learn to determine what your stats will be, and for how long during what buffs. Then you can start piecing the DPS chunks together. I'd recommend learning how to use Shadowcraft to accomplish this for speed and time concerns, but SimC should do the same thing. You'll just need a lot more time on your hands if you want a lot of iterations for those smooth distributions and smaller error margins.