I'm not found of bets either.
It just doesn't make sense to keep on 400 when they can push without a single problem nowdays.
They are there to make money, with 500 they are able to do more/lose less, and they'll definitely go that way, same for MS.
Regardless of XBX being an upgrade, the fact its selling better than the XBO for that price shows the market already fully accept it. Also does the surge of smartphones prices as I mentioned.
Long gone are the days of PS3 $599 disaster reveal, nowdays $499 for a very wanted piece of tech is nothing.
There is not a single reason for they to keep on 399, unless they want to REALLY bleed money to screw MS, which they don't need at all.
Anyway, want to make a bet without consequences then?
Whoever is right just need to come to the other to say he was right.
There will be problems at $499. The premium consoles did nothing to change that perception. If anything, they provided a way to sell at that higher price, while leaving the expectation on the table for affordability with a base model.
As for the Xbox One X selling better than the XBO, I've not heard anything like that. It is the 'S' model that brings in most of those sales, as I understand it (which is also secondary, given Microsoft doesn't release any specifics).