I think Thunderlord will be able to change element based on the Subclass equipped, not like how Murmur does it by switching perk nodes.
This is only possible since they are adding the new subclasses.
I got the idea from how Bishop from X-Men DoFP charges his weapon with his power. (Movie was meh except for Quicksilver)
Edit: changed title to better convey message.
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FIRELORD NOW