Ok, so I just got my first mage to max level today and switched to Fire. The current Combustion is kinda boring and all it does it give you guaranteed Pyroblast procs as well as some extra tick damage.
My idea is to make it so the crit and mastery bonus it gives you is either less or completely nonexistant and instead... Make Fireball an instacast spell that you can spam on the gcd.
I think this would make Combustion a lot more fun because it makes your burst phase different from your regular rotation and it makes you really feel like you're on fire like you're just spamming the shit out of fireball and you're like "cmon cmon crit you son of a bitch" but everything's so much faster like you're an insane pyromaniac which I feel really fits the class fantasy of "engulfing yourself in flames" as the tooltip for combustion says.
EDIT: also it would make sense if Flamestrike could proc Heating Up off crits like Pyroblast does so you can get Flamestrike chains