Going back to January this year has been planning about shipping KDE SC 4.13 in the next (K)ubuntu release. As of today, there's been mass package updates pushing all of the KDE components up to their latest 4.13 development versions; KDE 4.13 Beta 2 was released a few days ago.
The many KDE packages in the Ubuntu archive were bumped to their latest 4.13 development (4.12.90) development state upstream by Jonathan Riddell. The packages are currently in trusty-proposed and assuming no major KDE 4.13 issues come up during testing where they would have to revert to KDE SC 4.12, this will be the desktop version found in Kubuntu 14.04 LTS. The latest Ubuntu 14.04 "Trusty Tahr" package changes can be found via the trusty-changes mailing list.
Among the KDE 4.13 changes are Baloo replacing Nepomuk, C++11/C++1y syntax highlighting for the Kate text editor, Kate D language completion, various other Kate text editor improvements, many updates to the KDE PIM stack, KMail improvements, and many changes to the Palapeli KDE game. More details on the KDE 4.13 changes can be found via the KDE.org Techbase. KDE 4.13 is expected for a final release on 16 April while a third beta is due this week and a release candidate next week... Given Ubuntu 14.04 LTS is releasing the middle of April, the Kubuntu maintainers will likely be trailing these package updates quite closely and hoping for the best. Thanks to Phoronix reader Fabio Correa for pointing out the mass KDE update today in the Trusty archive.