Depends on whether Apple barely meets projected 1Q revenue or knocks it out of the park. If Apple crushes earnings then expect the X plus to fetch $100-150 more than the current X. If earnings come in soft then X plus could come in at the X's current price.
Apple, of late, however, has not backed down on pricing. It jacked up the price of the iPad Pro 9.7 (from the previous Air 2) and then jacked up the iPad Pro 10.5 and 12.9 256GB models months after it released them. Apple TV 4K pricing, in the face of monster competition of lower priced streamers, remains sky high, with no real benefit over the other streamers (that I can tell, except maybe Airplay capability). Mac pricing, in every category, is not too attractive for the included components.
So I would not hold my breath that the X plus will start at less than $1099 for 64GB. (I would also not hold my breath for a 128GB model because that would be the sweet spot for too many buyers and Apple wants to upsell. The perfect way to do that is the current line up of too small and too big.)