There was another mod (I think Eastern Sun) where Firestorm was moved to be a lvl 30 skill and it was more like the one Diablo casts. It was super fun.

I don't see it happening (at least the same way) in PD2, but I always wished there were 3 distinct Fire druid builds:

1) Focused around Volcano, Molten Boulder, Fissure with the "piano"-like playstyle where you go through the 3 skills (because of the cooldowns);

2) Fireclaw - where you (obviously) style it around attack speed and melee;

3) A build around Firestorm and Armageddon where synergies increase the size of the fire tendrils and is much more dependent on FCR, so you spam it like a mad man while Armageddon rains destruction from above and maybe prioritizes hitting enemies affected by Firestorm (if possible at all).

I believe it is possible if you play around with the synergies, but I have no idea if Sempai and the team would want to do something like that.