The problem with being GCD locked is you change from "best priority on abilities to manage resources and do damage" to simply "what is the highest dmg ability per GCD"
Its really bad for Death Knights since our runes and by extension there regen act as mini ability cooldowns, and without that we devolve into some pretty horrible game play like diseaseless blood in Wrath, where pressing frost fever and plague strike were not "worth" the GCD, parts of our class break down more so then some other Melee specifically Warriors and DH it doesnt really apply to them because of the nature of how those specs work.
I imagine if that Death coil change goes live on release it will be reverted in the following tier and mainly used as a band aid to get us through the extremely low haste values we will have early on in BFA, i would prefer a more well thought out fix that wont have UHDK posting "nerfed again" in patch 8.2. But again if they really want to force people to play with 16% haste in heroic/mythic Uldir then this might just be the best short term solution for that.
Development cycles are what they are. Blizzard has made a complete shit-show of a lot of once proud classes this xpac. Why should I trust they'll get their act together in the 3 months before launch?
And shepherds we shall be...