Blizzard talked about changes to Mythic+ Keystones in Patch 7.2.5. The depletion mechanism will be removed. If you don't finish the dungeon in time, you'll get a a Keystone for a random dungeon that's 1 level lower than the one you used.
Completing the run within the set time frame has the same effect as in 7.2. You get a Keystone that's 1-3 levels higher than the used one. Rewards are also on their radar, because players used lower Keystone runs to get best rewards. Finishing a Keystone will reward two items and an AP token. If you beat the timer (regardless of how quickly), the final chests will give you a third item reward.
Here's what blizzard has to say about this:
We’ve been thrilled to see how positively players have responded to Mythic Keystone dungeons since Legion’s release. However, there are a couple areas in which our original design for the system hasn’t quite matched up with how things have worked out in practice. In an upcoming 7.2.5 PTR build, we’re going to try out a couple of changes to how Keystone runs work.
The first big change is that we’re getting rid of the depletion mechanic. We’d originally imagined that getting ahold of a Keystone would be more of a barrier than it is, but in reality, there are so many players participating that it’s generally not too difficult to find someone with a Keystone you’d like to run. In that environment, depleting a Keystone is more of an annoyance than anything else – especially when it happens for reasons outside of your control (such as a player disconnecting).
Instead, we’re going to try the following:
Completing the run on time will have the same results it currently does in 7.2: you’ll get a new Keystone for a random dungeon that’s 1-3 levels higher than the one you just completed, based on how quickly you finished.
If you complete the dungeon but don’t make the timer, you’ll get a Keystone for a random dungeon that’s 1 level lower than the one you just used.
If you don’t complete the dungeon at all, you’ll have a Keystone for the same dungeon that’s one level lower than the one you just used.
The other thing we’re looking to change is the way that rewards are given at the end of a run. Currently, when you complete a run that upgrades your Keystone by 2 or 3 levels, you’re also given a 2nd or 3rd chest. This is because, when we believed that Keystones would be rare, we didn’t want you to miss out on any of the loot you might have collected from the runs you were “skipping.”
However, because of this, players tend to look for lower-level Keystones that they can easily stomp through, instead of higher-level Keystones that are appropriately challenging for their gear and skill. That, in turn, affects who they’re willing to invite. AOE damage output is preferred over everything else, because the only concern is how quickly you can clear through easy trash packs. And gear requirements tend to outpace what actually drops: if you could find upgrades in a Mythic 6, you’ll have a hard time finding a group, because the Mythic 6 groups are full of players who are capable of clearing 10+ and are just looking for an easy 3-chest.
With that in mind, here’s the changes we’re planning to test:
- You no longer receive additional chests at the end of a run for completing it quickly.
- When you finish a Mythic+ dungeon, the chest at the end will contain two items and an appropriate amount of Artifact Power.
- If you beat the timer, regardless of how quickly, there will be a third item in the chest.
- Keystones can still upgrade by 2 or 3 steps, so you can quickly get to a difficulty level appropriate for you.
Our overall goal with these changes is to incentivize groups to take on dungeons where they know they’re likely to see upgrades, instead of preferring keys that are far too easy for them. Once the Tomb of Sargeras raid is available on Mythic difficulty, we’ll also increase the maximum rewards from Mythic Keystone runs to level 15.