Sky Watcher would be a great addition (and definitely seems like he would be better than Iron Bull) but I don't think putting Avvars in games located further north is a good idea. The North (other than Tevinter) is mostly unknown: There are those burial rites of Nevarra and their mortalisssi. If I understand correctly, they have a special (somewhat priestly) order of mages, combined with practice of burying dead with intention of leaving the body to a spirit posessing it when the soul departs... How exactly does combine with Chantry teachings? Then there are city-states, Antiva, Blighted Anderfels and, in the east, the mistical Rivain where three different cultures somehow try to coexist...
There are just too many things that should be explored to drag in Avvars too. Avvars were, unfortunately, a wasted opportunity - they would be a great addition to Inquisition (much better than this somewhat out-of-place Qunari) but since they were not really included beyond legend of Trydda and custom of painting enemy's house with goat blood - I think BW would do better to leave them out for now altogether.
Unless they include them in some expansion-sized DLC to Inquisition, that is.
Still, I definitely agree, Sky Watcher seemed like a great companion opportunity, it's a pity he wasn't really recrutable. And it would definitely be nice to see a non-andrastian (but still rooted in SOME culture, unlike Morrigan) human perspective. Avvars seem like fun