For those interested in reading more about mega texturing, the wikipedia article has a nice, concise overview:
http://en.wikipedia.org/wiki/MegaTexture#cite_note-1

Here's a nice PDF on the subject with shiny pictures!:
http://s09.idav.ucdavis.edu/talks/05...Challenges.pdf

As the Mega Texture technique was demoed on the iPhone4 (notice I didn't say iOS), they likely mainly use Open GL ES 2.0 API, and arm cortex A8 optimizations and OMAP optimizations (PVR SGX 535). As such, I suspect porting this 'engine' would not be terribly difficult to other OSs (ie. Linux == Android), though a full game port is another matter entirely.

While I suspect that game will likely remain iOS only for some time, if android continues to grow, and the device portfolio continues to expand, Android development will likely follow shortly. Hopefully the team is considering cross-OS development as the underlying architecture across devices is largely identical.

Sadly, as Carmack's development is known as monetarily motivated, I can't foresee Nokia or RIM taking advantage of iD's push into the mobile space. Of course, this is just *one* title, so it's not a huge loss. Still to have such magnificent technical work on a platform is something to be desired and generally spawns competitive pressure for further development.

As an aside:
The wikipedia also mentions something to look out for in future Carmack developments as well. This is namely Sparse Voxel Octrees. This technique is basically similar to Mega Textures (or Virtual Textures) in that a very large and detailed geometry structure is streamed as necessary into the scene, and based on the rendering target, the geometry is determined using ray casting to minimize overdraw. This offers the possibility of automatic Level-Of-Detail, lower memory requirements, and geometry complexity that is more coupled to disk storage limits than memory/GPU limits! Wow. Coupled with Virtual Textures, this would result in quite the boost in a scenes complexity without a huge impact on performance approaching a polygon to texel ratio of 1.
http://en.wikipedia.org/wiki/Sparse_Voxel_Octree

It's remarkable watching it all happen. That we now have PS2s/XBoxes in our pockets was predicted years ago as we understand technological advancement. Still it's interesting to see how this vision unfolds. It's only a matter of time before we have quality like Avatar running in real-time on our hand-held devices as well, in 3D no less.