I'm probably going to invest into Breach and Blight as they'll be good for levelling early and could yield some decent rewards on the side. I'm also very tempted to invest into the Harbinger nodes, having one in every single map will start to add up for ancient shards and potentially exalted shards. It looks like you can get 100% increased chance to drop an additional shard, 30% chance for an additional Harbinger and 25% chance for a boss, there's also the line 'Currency shards dropped by Harbingers in areas can drop as currency items instead'. So maybe a very small chance of full ancient orbs and exalts dropping there?