I wonder if OS X itself would be tweaked a bit to facilitate enhanced power efficiency. An Air with long(er) battery life + Retina + decent crunching power could potentially threaten the "Ultrabook" segment.
The first thing it needs to do is put more RAM in the thing, even more so because it can't be upgraded over time. There really needs to be a 16GB BTO (and if there can be a 32GB one even better, even if it costs an arm and a leg, 16GB is not enough to be comfortable when you need to juggle half a dozen VMs)
It'd be cool if we could "power down" some RAM dynamically, energy saver modes and so forth.
Despite all of the sponsorship from Intel, it also wouldn't surprise me at all to see Ultrabook OEMs trailing Apple by weeks/months getting Haswell based stuff out the door.
Not exactly an ultrabook, but thinkpad x220/x230 was pretty amazing except for the low screen resolution. IPS screen, great keyboard, great performance aside from integrated graphics, space for an mSATA SSD as well as SATA HDD/SSD, battery slice to boost it to 20+ hours, removable battery, and great linux support.
I've got a mid-2010 mbp 15" that still works just fine, even if I could use it to cook food at times (any time the power adapter is hooked up), I guess I will eventually have to replace it but with an SSD and 4G ram it's doing just fine at the moment.
The one and only complaint I have is the low resolution, but 768 is not that bad on a 12.5" screen.