From the patch notes:
Problem:
Ignite builds don't have a way to focus their damage on bosses, forcing balance to be the same for clear speed damage and boss damage.
Solution:
Change Flame Surge and introduce a new attack-based mechanic to be able to deal much more Burning damage to a targeted enemy.
Specifics:
Flame Surge now creates a burning ground that deals damage equal to a percentage of that ignite if you hit an ignited enemy. Burning Ground can be created every 2 seconds, with a percentage of Ignite Damage on the enemy converted to Burning Ground.
Did they reveal what mechanic this is? Feels important for build planning.