I'm not to sure the spike will be that large. When the 20gb Pro (by far Microsoft's best selling SKU, over the Arcade and Elite) dropped to $299, sales only spiked to 90k, and the following week they dropped to 75k.
Unless the Arcade really takes off in demand at $199, I don't think this price drop will do much more than the previous drop. It may do even less, considering that some of the demand was met with the last price drop before stock ran out.







