I really think buffing Sunfire Cape's damage is not a good idea.
Unique Passive - Immolate damage increased from 11 + 1/lvl to 20 + 1/lvl (12-29 to 19-38) bonus damage to minions and monsters lowered from 200% to 100%
Given how dominant Sunfire Cape used to be (and how it insured the most common top lane picks in competitive were tanks fighting each other with wet noodles), I don't think buffing that aspect of the item is a good idea. Especially with the fact that everyone playing against those tanks effectively lost 12 MR.