I hope this suggestion is possible codeable and hopefully not imbalanced.

1) When there are only 2 enemy targets present, Chain Lightning should bounce back and forth between them (like lich chain frost and WD's casks)
When there are less than 4/8 targets, the chain lightning should completely bounced the full 4/8 times

2) Chain lightning should not have a cooldown. That means even before the full 4/8 jumps are completed, another chain lightning should be able to proc yet again