Personally, I agree with the devs that cast-while-moving has become too ubiquitous. Shadow priests have complained bitterly that they lack such abilities, and thanks to DoT snapshotting they can't often reapply their DoTs while they're on the move. But it should be the case that ranged and casters have a penalty for the advantage of being outside the melee fray. The trade-off should be that you can't wander freely around while doing damage, whilst also having the advantage of easy target swaps and a clear view of the battlefield, not to mention being easily able to actually stay in range of a moving target. The trade-off, historically, was that ranged were short on instants and largely had to stand still while they cast. Although it's still true for several ranged, there are others that don't suffer this at all. And that's too powerful.
Hunters, warlocks, shaman, anything with a bunch of instant cast spells, I'd like to see nerfs to all of them. Restore the old balance where the trade-off existed. Ranged DPS should not be able to execute their entire rotation on the move. Lore's follow-up tweet is also very indicative of Blizzard's angle on the whole squish. They're not buffing all the classes up to meet high outliers, as they have before which was the approach that got us into this whole mess. Instead, they're pulling classes down to meet the lower end. And that's a good thing.
Casting on the move is something we've talked about a lot, and we're definitely making some changes along those lines. I don't have any details I can share at this point, but I can at least give some insight into our thinking.
We like casting on the move, but not as a default. Spiritwalker's Grace is a good example of something we like; used intelligently, it can be very strong, and it feels good to use. On the other hand, Lightning Bolt always being castable on the move we're less excited about. You don't feel smart or skilled for using Lightning Bolt while you're moving, it's just sort of a free bonus that we're not sure is really needed.
Things like Kil'Jaeden's Cunning fall somewhere in the middle. The effect is similar to Lightning Bolt in that it's always active and you don't really have to think about it. However, you are effectively giving up either Archimonde's Darkness or Mannoroth's Fury in order to take it. Whether or not that's enough of a tradeoff is something we're discussing, but we have seen a lot more Warlocks giving up KJC for something else since Patch 5.4.
It's also important to note that the ability to use a cast-time spell while moving is only part of the issue. In fact, while there's only a couple of classes that can do that, almost everyone has some number of instant cast spells they can use while moving. To really start shoring up the differences here, we need to reduce the number of instant cast spells as well. That includes healers.
We're still iterating rapidly on all of this, so anything can change at any point, but that's what we're currently thinking.