Since ppl are saying this is not a great 45 points talent, so i come out with this idea:
Fire and Brimstone (Rank 3)
Increase the damage by your Immolate spell by an amount equal to 15% of your spell power, and the critical bonus damage of your Conflagrate by 24% if Immolate on the target has 5 or fewer second remaining. In addition, each time your Immolate deal periodic damage, it has 15% chance to cut your next Rain of Fire spell's channeling time into 4 seconds(tick every second), but no longer require you to channel it with no mana cost.
Pros: 1. Make Rain of Fire more useful in raid situation since boss is static, you can make sure all ticks hit the boss.
2. You do not have to channel it, so you can cast another spell while having Rain of Fire dealing GOOD damage on your target (I heard its coefficient get buffed and can crit now, thus benefit from critical chance and Ruin.)
3. Free of mana cost.
4. 3 ranks, free up some talent points.
Cons:1. This spell will not as op as you think in PvP because you can simply run out of it.
Thank you for feedback.
Improved Immolate (Tier 5, Rank 3)
Increases the initial damage of your Immolate spell by 30%. When Immolate get dispelled, it will afflict the dispeller again with (33/66/100%) of the duration and each time the dispeller cast a spell, he/she will get 812-1230 Fire damage and 4% total mana burn. (Pro tips: Don't dispell it anymore.)