*Spoilers* about the scions....

[Bonbori]

The Japanese VO, to me, sounds like a cross between Urianger and Alphinaud? Like I think the underlying timbre is more like Alphinaud's voice actor's, but the hoarsness reminds me of the way Urianger sounds. Perhaps it's an alt reality version of Alphy who's... either seen some stuff or hung around Urianger for too long? I'd go with the latter, too much Urianger messeth with thine brayn, forsooth. Verily.

Gumption.

Ahem... For comparison, here's the 4.4 trailer (~2:48), Urianger's sample from AAR (0:50) surprisingly hard to find anything more recent, and Alphinaud from 4.3 trailer (1:07).
As for the WoD theory, I can see that... but I'm not 100% convinced. The actor's underlying voice doesn't quite sound like Arbert to me, but it's been a while since I heard him in the game so maybe I need to hear more samples to see it. Alphy's and Urianger's voices are much much fresher in my memory. Anyways, for the sake of completeness, here's him and post-HW Alphinaud side-by-side (8:51 and 9:54 respectively).

There's also a high chance that we're totally overthinking it and it's actually a new character.