Please use the search function. There is discussion regarding this in the thread you posted in.
Mastery obviously isn't being nerfed. Base mastery is simply being lowered. (think of a linear equation. Now think of base mastery as the y-intercept. When the y-intercept is less it doesn't change the slope; i.e. the value of mastery in this case)
Now, onto the stat priorities. I have read that the priority will become Str > Hit to 8% > 26 Exp > Crit > Hit to 27% > Haste >= Mastery. All speculation though, credit to Landsoul. (he posted these stat weights on the official forums) As for Slam, I do not think it will be better than RB for TG; seeing as how it's only better than RB for SMF since it hits with both weapons. TG slam still hits with one weapon.
Edit: Of course this is all just inferences, so nothing is set in stone.