I see no good reason it was removed and non that stops bringing it back. It was an amazing spell that gave you the option of buffing other utility abilities in return for a shard (say soulburn: demonic teleport made you 50% faster after teleporting to your circle. Soulburn: Drain Life made Drain Life do significantly more healing, etc). It only took one extra ability on the bar but allowed for so much options
Depending on the expansion, it also had dps applications, ussualy along the lines of "you sacrifice shards for inefficent burst in cases the mob wont live long enough for regular rotation", such as Soulburn: Soulswap allowing you to apply all your 3 dots in the span on a single global.
In current design, we could have Soulburn: Agony (applies all baseline dots, including unstable affliction, and Siphon Life too if talented) for one shard, maybe two. and Soulburn: Seed of Corruption to make seed cost one more shard (so 2 total), but be instant cast and also explode instantly. This won't make afflocks dominate burst, but it will give them actual (if inefficent) options when mobs die quick, which is perfect for a dot specc that isnt meant to excel in burst. Most importantly, it will add fun and intelligent decisions without disrupting anything else.
Thoughts and opinions welcome.