kde3.5.9 - look into /usr/kde/3.5 and /usr
kde3.5.10 - look into /usr/kde/3.5 in order to remove issues with kde4 with -kdeprefix
kde4 -look into /usr or /usr/kde/4.1 based on kdeprefix

solution:
update eclass so it installs into /usr/kde/3.5
revbump all misc packages that use kde eclass. // might be done by recursive script searching for packages with kde inheritage. // note need testing tree, maybe puting whole tree without log to kde-testing branch.
Make sure this packages are stabled before stabing 3.5.10

approach for migration to kde-testing:
we use script that converts all misc packages by once. this script must have expections for packages wich would be needed skiped. must be portable between git and cvs so we can use it in the end for commit into portage.
List of packages which makes trouble would be created their patches will be done and then individualy commited back to the tree. Who will do this if it will be to much i dunno.

If you have some notes/questions point them on #gentoo-kde.