Sure. Let's go over to this shiny new thread.
First you have to contend with the iPhone—how much can it do? A lot, frankly, but it fails in two areas: long term use & laptop replacement.
Then you have to contend with the MacBook—how much can it do? Most anything, constrained by time to crunch CPU/GPU cycles, but it lacks the battery life of a scaled up iPhone & lacks Mutitouch.
So you could have a tablet, which is 10" MacBook - keyboard - OS X + Mobile OS X.
The main problem then becomes convincing customers to accept that this tablet is not like a Windows tablet, and it requires completely different/new/redone programs and you can't just use OS X stuff.
You now also have a very wide gap between the iPhone's power and the tablet's power: do developers target the iPhone or the tablet? Both, but separately? Or are they just locked out of the iPhone despite now having a SDK for Mobile OS X?
You could just stick OS X on the tablet and bolt on Multitouch but it wouldn't work that great I believe (too much UI redesign would be required, and Apple couldn't force 3rd parties to do it), and your battery life is going be the same as a laptop. Still great for vertical markets (and would kick Windows ass, natch) but not something to get people to ditch their laptops for.
Go down to 6-7"—that is Newton size, and certainly lighter—and you have something that is clearly not viewed as a computer so Mobile OS X just makes sense. Furthermore it's much closer in hardware terms to the iPhone, so that helps developers.
It's got power to run iMovie '08 I imagine, or a stripped down version, along with other basic multimedia manipulation and all the other stuff (email, browsing, eBooks, typing) benefits from the much larger screen. Furthermore without the cellular radio always being on you can probably hit 24 hours of battery (as long as WiFi is off, of course) and that is the big difference.
If I could have something that replaces 60% of what I do with my laptop to start, and 90% later as the lightweight versions of OS X programs are ported over and I add an external keyboard, as well as weighing a quarter of my laptop, being smaller in every way, and only needing a charge once a day? I'm sold.
The iPhone price drop and the old Newton shows you can probably hit $700 for this by 2008 (flash prices, mostly) and maybe a bit lower. Once these things sell enough and have a good software library you bring back the eMate (i.e. Mobile OS X in a 10" laptop form, with touchable screen, same 24 odd hours of battery life) & perhaps a 10" tablet form. Heck the eMate2 & a tablet could have the exact same hardware/screen just with the eMate2 having a keyboard.
I remain unsure if the 10" tablet would sell, given the Newton2 at 6" and the eMate2 with a keyboard at the same size, but as long as it and the eMate2 share parts it won't need crazy good sales just solid ones. I'm sure vertical markets would love a 24 hour tablet without the crud of Windows.
My way gets developers on board first for the iPhone and the 6-7" model (maybe 6" would be better, now that I think about it) and then with a solid application base you expand upwards to the 10" laptop & tablet spaces.
A modern subnotebook might be faster then our eMate2, but eMate2 has 3-6 times the battery life and is a third the price. Same difference in the tablet space once you've established the difference between a Macintosh, and an Apple OS X device. I think you have to establish that difference carefully step by step, rather then dropping in.
 I wouldn't want to read an eBook, or spend a long time browsing websites, or hook up a keyboard and type for a while on an iPhone. I used to think so, but having played around with a friends iPhone (lousy Rogers in Canada not letting me get one) the screen is just too small for longer term use. Great for what it is, not so great to be a laptop replacement.
 Email, web use, typing, multimedia, light multimedia manipulation, and games. I'm talking more about the people who do that, over those who actually use the power of their laptop (since that's a small fraction) because of their work.
 The level of work it would take to redo the entire OS X interface + programs so they could properly use Multitouch is vast. Multitouch is something very well thought out, most of the time, and to continue to use it like that would require OS X to be completely redone. Otherwise it's a level of usefulness below that of Windows/OS X + pen, since a stylus can simulate a mouse better than a finger.
 Yes yes the Foleo. It lacked battery life, applications, and multimedia. With those, plus a good design & not requiring a Treo, it would have been a great machine.
 First the iPhone, nothing to do with the Mac. Then Newton2 like a scaled up iPod Touch/iPhone - celluar radio. With the Newton2 you release the SDK for Mobile OS X. Then a little while down the road with an application library and iPhone/iPod Touch/Newton2 doing computer like things without being 'Macs' you can expand towards Macintosh computer size with eMate2 & a tablet.