Good points on price and stock. Microsoft can get really aggressive with price and discounts. We'll see.
MS really likes to muddy the waters, so I could see Series S being sold on a payment plan. Something like paying $30 a month for two years, and you get XBL Gold, a diskless Series S, and Gamepass. That would come out to about $360 per console, but MS would probably talk about "value" from now until the end of time. Roughly 30% of console users have online subscriptions, so for most people XBL would be a waste of money. But a lot of people would buy into that, because they don't want to pay $300 upfront, or buy games.