Patch 7.2 is coming this week (worry not, the new raid is still months out). If you routinely do a 15 keystone each week, you may want to do an 18 this week. Why? Starting with 7.2, each level will get more difficult, and a 10+ generates the maximum reward (of a 905 in your weekly cache).
More significantly to this post, for this week only, if you do an 18 you will get a 10 in your bags next week.
See this blue post for more information: https://us.battle.net/forums/en/wow/topic/20753795211#1.
Key you get next week based on highest key completed this week:
Mythic 2-8: level 2
Keystone Mythic 9-10: level 3
Mythic 11: level 4
Mythic 12: level 5
Mythic 13-14: level 6
Mythic 15: level 7 (each difficulty level above 15 increases next week’s Keystone level by 1)
Or, if you want to run lots of mythic plus next week for AP, consider doing only a level 10 this week, as that will generate the (maximum) 905 gear reward next week and you will start with a 3-level key you can run many times:
To put it more directly: completing a Keystone dungeon of difficulty 10 or higher this week will result in a reward with a minimum item level of 905 in your next weekly chest, which is the current maximum reward in Patch 7.2.
A tidbit for next week: Do the intro quest in the Broken Isles first thing, it leads to getting Artifact Knowledge 26 instantly, which increases AP gains by something like 400% over level 25.
Only after doing that should you
open your weekly cache (which rewards Artifact Power now) (EDIT 2017-3-27: the weekly cache will not reward AP the first week of 7.2), do world quests, dungeons, etc.
Do you know of any more things like this to do this weekend to be prepared for 7.2?