There won't be completely destructable enviroments, though I think trees can fall and burn, while snow can melt and stuff...
This whole environment burning doesn't extend to burning down trees i think it's like the effect shown in the trailer ie. fire on the object.
This is the quote this idea has stemmed from i think
"If you're wielding the flame spell like a flame thrower, the environment will catch fire for a short while and burn anything that comes into contact with it."
To me that just suggests a fire effect on the object and burning any animal etc. that comes into contact with it. So nothing to suggest destructible environments in my opinion.