As im looking it from my experience of the first reset with this low haste levels i dont see Burn phase much viable now. Due our high mana regen and draenor AP's perk the only time when you can use burn phases is if you use glyphed arcane power with overpowered tallent with hero on pull. In other cases you just burn as much as u are capable within 15 seconds, which is not much either for the same reason (low haste), discharge with Barrage and evocate till u get to 95%ish mana, interrupt the channel and continue the good ol' conserve rotation to not dip below 85-90%.