Hmm... Neither Hurricane nor Storm would do well paired with Vein, that leaves three remaining options,
A. Some random completely new character(likely an ember since we haven't seen much of those).
B. Chroneo, because Wildew deserved an actual life before getting dragged into his sister's mad, suicidal revenge plan and dying in an extremely dramatic way,
C. Qinter - yes I know he isn't a wyvern, but from a scientific standpoint, deinonychus and rock drakes share many features, suggesting a close relation, wyverns are even closer relatives of rock drakes, fire wyverns are a type of wyvern, either the ancestor, or the closest descendant of crystal wyverns, so technically Qinter shares something like 60% of crystal wyvern
making him a very small, fluffy, overly optimistic, maniraptorian wyvern.
(I apologise for any slight confusion reading that, I sometimes can't help sudden uncontrollable scientific outbursts)