From what i understand, it means that now the way you calculate dmg for the abilities listed at the bottom of the post, (SS,MS, and some others), is gonna be changed, right now when u use one of this abilities, it calculates the atck power bonus to this abilitie using your actual weapon swing time, now it wil use a set swing speed which depends on your wep, for example an Arcanite reaper will no loinger calculate its Mortal strike dmg with 3.8 sec swing time(not sure if its 3.8) it will now use a 3.3 swing speed, so the dmg of mortal strike will be less, wont be anything too dramatic, but still less, same for rogues SS, now all daggers will calculate their dmg with a 1.7 sec swing speed, this will lower the dmg of the SS if your wepp is above 1.7 secs, but raise it if your wep was below 1.7 secs.
Slower weps will still do more dmg with this abilities since their damage is still higher, blizz says its gonna make faster weps more viable, and bring down the dmg some weps were doing (AR is one of them).
This wont lower the dmg so much for Warrs and rogues wielding slow weps, according to the post is at most a 4-5% dmg reduction, which makes me wonder why they are doing it if its not too much to make a difference?