Apple has released CUPS 1.6, a major release that is supposed to replace 1.5.x branch. The version brings a lot of bug fixes as well as new features, such as Native Bonjour, ICC profiles through colord and D-BUS, Destination-Based Printing, Auto Authentication, and many more. You can read the changes on What's New in CUPS 1.6. Please note that Apple has removed a lot of filters and backend on this release which is no longer used in Apple Mac OS X, and those works are now being moved to LinuxFoundation's OpenPrinting project under cups-filters package.
I have prepared an updated SlackBuild for CUPS 1.6 on my SlackHacks under a branch name called cups1.6. For now, i will put CUPS 1.5.4 on my master tree and i will have CUPS 1.6 on my other branch because it's still a new release and major changes are happening on this, so it may not be suitable for most people, even though it works on my desktop. If you plan to upgrade to CUPS 1.6, don't forget to install cups-filters package as well or else you will loose a lot of filters and backends.
Please let me know if there's something wrong with the SlackBuild and i'm open for suggestions and improvements.