I think they'll adopt N, but I don't think they'll make it a differential feature, because it would cause confusion with regard to which laptops work where, and so on.... That's what I think personally, although in truth the penetration of WPA and 802.11g in hotspots is so low that.... *le sigh* it might not make a difference.
The only places where Apple has really used connectivity as a differential feature in the past have been FW800 (and the lower end computers all have FW400) and Gigabit ethernet. BT2 and 802.11g came out quickly for computers across the board. I hope that Apple will avoid the confusion of making some of their computers and hardware 802.11N and others not....
EDIT: FragTek, I think Airport Express cards are basically a dying commodity, right? The only Macs in which they really exist anymore are the PowerMacs, and that's only because they haven't been updated yet. I think we're only going to see integrated on logic board wireless from here on....