Hopefully Apple is paying attention to products like this. I'd love to replace my ibook with a more powerful, but smaller machine, and I really want to stick with OSX. I want my macbook mini.
Actually, what I would probably really like to see, rather than a tiny-laptop format from Apple, is a tablet that has a virtual split thumb keyboard. The Samsung UMPC originally had a virtual split thumb keyboard instead of the split real thumb keyboard. As you held the sides, and you needed to type, translucent overlay keys for the left and right thumbs appeared in the upper left and upper right corners of the display.
Then give it a removable fold under cover, that protects the screen, can be held flush against the back when holding it like a tablet, or used as a kickstand when at a desk (fold under == as you hold the sides, the cover folds under the bottom edge, not over the top; you'll see why when I get to the WWAN). 2 or 3 USB ports, micro-DVI out, audio out, power, wifi, express card slot, and bluetooth (DUN, PAN, FTP, real HDI and SPP to use any bluetooth keyboard, not just certain bluetooth keyboards) ... and _maybe_ a WWAN capability (or place the express card slot in a way that it doesn't get in the way of your hands when you hold the sides of the screen; so maybe it's on the top edge; if not that, then make sure the iPhone can share its WWAN with the device, either via wifi or bluetooth). I might also give it one or two full size SDHC card slots (it's really a staple among the UMPC and MID families to have some form of SD card, and doing it via USB is actually kind of annoying). Give it a screen around 8". No optical disk.
Typing on the go: virtual thumb keyboard.
Typing at a random table: bluetooth keyboard
Typing at your desk: USB keyboard
Let it do the same things for an optical drive that a MBA does (the one and only thing that I liked about the MBA is it's ability to "borrow" the optical drive of your desktop computer).
The reason the fold under cover is removable: let 3rd parties make keyboard replacements for the cover.
I think that's what I'd really want with a Mac based UMPC.
In the "2nd generation wishlist" I said a twist-screen laptop/tablet format, but I think that's actually slightly clunky. I'd prefer an actual tablet, like the virtual keyboard oriented Samsung (O2?) UMPC.