Obviously, KDE's katepart component uses floating point number for checking its plugins. So, if a plugin defines 4.3 it will be rejected because 4.3 > 4.10. For me, "highlight selection" plugin was affected by this issue. The patch that was proposed upstream (see URL) is working for me and should be added to a new kde-base/katepart-4.10.0-r1 ebuild.
Patch was accepted upstream and will be fixed in 4.10.1
Thanks, fixed in CVS. + 11 Feb 2013; Michael Palimaka <kensington@gentoo.org> + +files/katepart-4.10.0-plugins.patch, +katepart-4.10.0-r1.ebuild: + Backport patch from upstream to fix loading of the highlight-selection plugin, + wrt bug #456660.