I think a $299 Xbox One would at the very least sell on par with the PS4 in NA, but most likely outsell it. However, on a global scale, the PS4 would outsell the Xbox One on weekly basis.
I dont know, seems similar to the notion of "at 399 X1 will match PS4 sales" and it failed to do that.
360 cost 299 399, PS3 499 599
A 360 could have been had for Half the price of the top PS3 sku. Now 360 had a proper price advantage, among many others. X1 at 100 less is still an X1 with not a single other advantage really.