“The release schedule for KDE 4 is now clear, and it will be released
during the development cycle of Kubuntu 8.04. This new major release
is already attracting significant interest from users, and is the
focus of most KDE developer effort at this point. The majority of
enquiries are now about KDE 4, and an unsupported Live CD of the 7.10
platform with KDE 4 RC2 we released earlier this month was downloaded
by a significant number of developers.

We regularly review each release during the development cycle, keeping
an eye on the work that our upstreams are doing. From time to time,
this work reaches a natural rest point resulting in a particularly
stable release. For these releases, Canonical makes a commercial
commitment to provide support for a longer term and these become known
as “LTS” releases.

Since KDE 4 is a major change to the platform, it is not currently at
one of these natural rest points so would not be suitable for long
term support. Instead, due to the very high interest, development
efforts will be directed towards KDE 4 and releasing Kubuntu 8.04 with
the option of using either KDE 3.5 or KDE 4.

Users currently running Kubuntu 6.06 will be able to upgrade through
the usual path to Kubuntu 8.04, keeping to the KDE 3.5 release series,
and will receive the usual 18 months of support for that
release. Future Kubuntu releases are likely to be based on the KDE 4
series.”

Quellle: https://lists.ubuntu.com/archives/kubuntu-devel/2007-December/002066.html