Thanks for following up on this; I feel like you and Alex are something like rock stars in the WordPress community, and I’m always hesitant to approach such people directly. I have a great deal of respect and appreciation for the work both of you do and hate to imply that it’s not sufficient :-\ (Because it is! Sufficient and wonderful, that is.)

While I can understand the concept of what you’re saying, I’m not certain I am capable of writing such a thing myself. Regarding serving a separate cache file, I’d wonder how you address the issue of search engines indexing the second cache as duplicate material; Milorad seems to provide a potential solution to this, but I haven’t gotten it to work yet.

If I can figure out how to modify something like WordPress Mobile Edition to 1) Set up a separate cache for mobile devices, 2) Automatically edit .htaccess to input the UA strings for mobile devices, and 3) Automatically edit robots.txt and/or setup a separate robots.txt file to prevent indexing of the mobile cache, I’ll certainly let you know… In fact, if I could even figure out how to do it without a plugin, I’d write about it. But I’m not altogether certain that’ll happen anytime soon

In “half on” mode, It would be easy enough to write a plugin that checked the user agent string for the iphone and served a different cache file. In full on static caching mode, the blog author would have to modify the mod_rewrite rules manually and add in those user agent checks.

I hinted at this in my announcement post here: http://ocaoimh.ie/2008/11/25/wordpress-mu-265/ but nobody seems to have picked up on it.