With 7.2 going live next week, you´ll get a nifty AP token from your weekly mythic+ chests from now on (PTR currently: 1,2 million at AK25 from a 15 Mythic and a 900 TF item).
Now if you do a Mythic 15 this week but dont loot the chest on patch day, instead you can start all the necessary quests from the broken shore, one of them sends you back to your order hall and lets you upgrade your AK to 26 and start further research. You get AK26 instantly, which is a substantial buff:
AK25 24.900%
AK26 100.000%
a fourtimes increase -
you can see the difference here at 1:44: