Are you thinking of making him a shadow sorcerer? I think, that would fit.
Oh yes, or at least multiclass into it, as wizard / wild magic Sorcerer is one of those odd mixtures, I very much enjoy. We'll probably have plenty of chats with Withers once the patch releases.
Bladesinging also sounds interesting, not to make the Shadow Weave felt but in general - and for the shallow reason that I like to hear Gale's dipping comments more often. ^^
I think, it's pretty relatable, that Gale would look for other methods to do magic, since the orb should really make it impossible to reach into the weave as a mage. I made an all bard playthrough and thought, that Gale would jump on it (in early access he had a dialogue with a bard Tav that he is trying to write a book).
But shadow sorcerer sounds pretty fitting with it's darker theme.
I contemplating to make Lae'zel a Bladesinger, since that would fit her as a gith.
