I must admit... this is upsetting.. I've been developing a cold build since RoS launched, and this skill and rune has more or less been the staple.... now I can't use it.... why would they change this rune to fire?
Because they wanted to make more abilities be options for multiple elements. You'll notice they did it for a lot of skills, across all classes. Fetish army with a cold dmg option, etc.
You should have plenty of time to finish your build and get sick of it before the patch launches and you can try new stuff. Though... perhaps not if you've been doing it since RoS launch. Maybe you should try new things now, that's a long time to be doing the same build.
I'm still waiting for a halfway decent selection of physical signature spells. Hell, 2 or 3 would be enough, especially one for plague of toads. Locust swarm getting some other options is nice, now haunt needs a fire and/or poison option. Even rend got elemental leeway and it's a damn bleed. I understand suspension of disbelief, but not at the cost of fun and differing gameplay styles. I'd like to see it broadened a lot more before the PTR's done.
It's just unfortunate that fire builds already do pretty beef stick damage... this is one of the only damaging cold skills next to haunt... I made the cold build to get away from the physical/fire/ pet builds.. now I gotta change to fire so my spirit barrage rolls on items through the enchantress aren't wasted.... ;[