The cost of Power Word: Shield is being increased by 33%. While we wanted Discipline priests to be able to utilize this spell more often and with better results, we also did not want it to be the main spell (and often the only spell) used while in groups. We don’t find this to be a particularly compelling playstyle and have found that it encourages players to avoid using other spells such as Penance. We believe that using a shield in a tight moment is totally appropriate, but we don’t want it to be incredibly efficient to do so with more frequency than that.
We realize that by making Power Word: Shield slightly more expensive for Discipline priests to cast that it might cause Holy priests to avoid using it. To that end, we are adding mana savings into the Body and Soul talent. The tooltip will not reflect this change until a future patch, however. Ideally, Holy priests should not notice much of a change to the Power Word: Shield costs.
the suggested change to Power Word: Shield is a direct nerf to Discipline's Mana longevity.
The change, as written, will HURT our ability to last through fights while doing NOTHING to address the spam issue.
as presented in the blue posts, VERY well geared Disc priests will still be able to spam Power Word: Shield, they will simply have to make use of cooldowns more often (using the haste conversions for Hymn of Hope and Shadowfiend, and using trinkets like the Core of Ripeness and the alchemy trinket).
In fact, increasing the cost of healing will hurt single target healing somewhat, but shield spamming will STILL be viable with a gear change: Intellect -> mastery -> spirit, and avoid crit and haste at all costs. This pushes priests FURTHER toward raid-spam of bubbles.
Why not an increased cooldown? 6-8 second base cooldown, with Soul Warding reducing the cooldown by 1/2 seconds still (down to 4-6) seconds would let disc priests cast shield on multiple targets, but the cooldown would make shielding even an entire heroic group difficult or impossible.
If the problem with Disc priests is mana longevity is lasting too long, then this change is relatively in-line. If, however, the problem is the playstyle of using one spell to the exclusion of all else (as stated in the blue post), then please address that by actually making it physically impossible to cast a shield every 1 second, but don't nerf the mana longevity of the entire tree (heck, you could even add a 15/30% mana cost increase on the Soul warding talent)!