I don't really know enough yet to have a firm opinion on the matter. While it seems that they're going for 'Asmo as fallen celestial', it risks being too close to Baalzebul's thing potentially, and potentially too much straight up association with Judeo-Xtian mythology, but the stress on the Blood War and the Law/Chaos axis puts my mind at rest over any chance of them stressing a Good/Evil axis too much. But it certainly puts a few nails in the coffin of the idea of Asmodeus being one of the original beings of Baator.
If they have him being a fallen Archon, ok, a bit expected, but ok. If a fallen Aasimon, Asmo is considerably younger than anyone previously expected. Maybe we'll see something completely unexpected, like Asmo being a fallen Eladrin prince who rejected both Chaos and Good.
I'm still itching to see how the Ancient Baatorians are handled, maybe some lore on the origins of Levistus and Dispater, and of course any tip of the hat to the Baernaloth myth w/ regards to the original inhabitants of the plane.