I tried it at 907 last night running prydaz/Chest legendary, its doable - i was getting to phase 2 pretty reliably, best attempt was ~15%. my current issue is trying to get a smoother transition between phase 1 and 2 where i dont have netherhorrors or as many infernals up.
Healing orbs seem to be more reliable now 8 out of 10 attempts im at least getting an orb before the first infernal.
Velen seems to want to melee more, which isn't necessarily a bad thing, he is unaffected by the puddle near the inquisitor.
Most of my deaths in Phase 1 were from trying to push dps and not grabbing the healing orbs when i should and die to the mindrend.
I've got another 30 attempts or so tonight, we'll see.