Yeah, I tried a few times - but I found that the Origins stories work *way* better as NPC's as they do the Main Character.
For one, the main character is silent everytime he/she needs to decide something. Then, there are these moments added like 'contemplate telling someone youér a Sharran' etc, which are pointless, because just like the Dark Urge: nobody cares. At least a Tav can care, and for that matter - a Selunite Tav has a way better Shadowheart Story than Shadowheart herself does.
Then. Romancing another NPC triggers *their* romance, just like Tav would, and not yours, so.. You miss out on the personalized content there, too. I tried playing as Gale for a bit, but couldn't find *any* Gale specific lines all the way into the Grove and rerolled. I had kind of figured you'd get another fun scene where he'd end up in the Portal and someone would pull him out, but.. No. Just the same stuff.