When I saw the first Slackware64-current changelog and saw the bump in icu4c, and all the packages that were re-compiled in response, I knew from experience that some of Alien BOB's packages would also be affected, and decided to hold off on upgrading until Eric had had time to re-compile some of his packages to match the new version.
After work, I saw an update to the RSS feed of Alien BOB's KDE packages, and lo and behold! New re-builds of packages were available. Also, there was a second update to -current. I immediately rebooted to runlevel 3, and ran the slackpkg update first, then upgraded Alien BOB's updated packages. There was not the slightest issue, after rebooting, getting back into the Plasma 5 desktop.
As usual, patience works well for these kinds of situations.
Just my