Packages in the summary should not block each other, otherwise kde-apps/dolphin:4, when built with KF5 has no mtp support. The packages have no file collisions and they co-exist without any problem AFAIK.
It looks like it no longer blocks due to path installation changes in extra-cmake-modules.
Ping. This is still true in kde-plasma/kio-extras-5.3.0
Thanks, fixed in git. https://gitweb.gentoo.org/proj/kde.git/commit/?id=0bd80237694c991392157898deb59820d3ae64e2