I don't understand this shift towards smaller screens. We've lost the 17" laptops which were great machines. Apple appears to be abandoning the 15" and shifting down to 11", 12" and 13" screens.
Is there any evidence that the 15" rMBP is in danger? If anything was in danger it would be the 13" rMBP which would be heavily canibalised by a 13" Retina Air - but it sounds like the rMBA is going to be 12", which makes for a sensible delineation.
I have a 17" MBP and its a great machine... but its still a hell of a lump to carry c.f. the smaller macs - both in terms of weight and fitting it in a bag. The more I look at the 15 and 15" rMBPs the more sense they make: a scaled mode that gives the same resolution as the 17" and the ability to drive 2 external displays. I'll be ready to switch to one once Broadwell comes out.
What would be useful is if Apple merged iOS and MacOS so that we still have the full power of the MacOS but gain the touch ability along with pressure sensitive brushes and pens.
Sorry, but I'm with Steve and Tim on the whole "gorilla arms" thing: touch/pen input only makes sense on a hand-held tablet, not a laptop, and both interfaces need their own UI. Try to merge them and, well: Windows 8, Gnome 3, Ubuntu Unity... I rest my case.
A laptop needs a touchscreen like a tablet needs a keyboard.
Pro-tip: a retina MBP
and an iPad will, together, weigh less than the 17" MBP...
An application to use an iPad (with a decent stylus) as a cut-price Wacom Cintiq would be good, though.
(* if I did, I might have to give up my pet air travel peeve: 'if its got wheels it ain't hand luggage' ).