If you play fire optimally you can't swap either really, you still want to have a high dosis of crit.
Even though some play mastery, mastery is useless with low crit %.
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About fire nerfs, I don't see them nerfing much, they might adjust things, but really nerf it, I doubt it.
Reasoning why they nerfed in the past was due to the high peaks you could get from snapshotting.
With that removed, fire damage will be more in line than before, thus not needing anything else but small adjustments.