integrating qt4/qtopia4 might be worthwhile IF you could be sure that you could, say, replace most of the standard apps with new qt4 ones, and yet have sufficient compatibility to still run the original Sharp apps. If you lose sharp compat, you might as well simply install angstrom with qt4 or opie2!
I agree that replacing as many of the kernel modules as possible with ones backported from later 2.4 kernels if possible, but that would be a lot of work; I think Anton did that when he build cacko1.23. And of course updating all the misc patches like ssh, busybox etc would be important - remembering that it all has to be gcc2.95.x compatible for the kernel and glibs!
So, actually, how many Sharp apps are actually worth keeping? Is it simply that cacko is a well-rounded system with working control panels for network, bluetooth, speed, overclocking, dialup, etc? How far off that is pdaXrom, Angstrom, Debian or Poky and would it be more worthwhile to make these work?