Based upon that experience and given a little more consideration, I propose the following mechanic: when striking targets affected by the Gloom (that is, gloom-based confusion, stun, and slow), generate a small amount of hate (approximately 0.03 would probably be most appropriate). There are a number of advantages to this:
- Not a perfectly reliable means of hate regeneration, so pursuing other sources is still valuable
- When fighting multiple targets, you may to make a tactical choice over focusing on a single target or trying to attack enemies affected by Gloom to generate hate
- Could scale with target rank so "cold encounters" with bosses are more approachable
- Easy to work into the current mechanics
- More or less equivalent to the other means for Cursed to generate Hate, apart from killing (cursed weapons and resource-leech equipment)
- Talents that hit multiple targets in melee gain extra utility (as does allowing yourself to be surrounded by multiple targets)
EDIT: 0.03 proved way too little to incentivize my gameplay choices. I have changed it to 0.1, and made it scale (directly) with target rank. Attached is the modified Actor.lua file (you will need to fix the extension); the relevant changes are in the onTakeHit function. Currently it does not check that any damage is actually done; that should probably change.
EDIT2:
I made it to Prox with my Cursed Higher (my typical choice, dwarf, was making it difficult to test that the skill was working). Of course, by the time I found him, my hate had worn down to nought. Thanks to the hate-on-hit mechanic, I was able to build my hate up high enough to have some moderate defenses and land the occasional Ruined Cut. It turned a probably impossible fight into a just-barely-survivable fight. Afterwards I max'd Gloom and just entered Norgos' Lair; we'll see how well this continues to play.