The first version of the KDE4 desktop series, KDE 4.0 is planned to be release in December, 11th 2007 and our releases managers are aiming to release Lenny in September. Given that there are some months between releases, this seem to lead a lot of people to think Lenny will be released with KDE4, but this is highly improbable. It is true that KDE 4.0 could be delayed again, and almost everybody is expecting Lenny be delayed… :)
The development of KDE4 started more than 2 years ago, and actually the libraries seems to be in a pretty good shape, the next release of the KDE Development Platform is a proof of that, a lot of stuff that is what the end user actually see, like plasma, needs still some work. A lot of improvements that we are hoping see in our desktop won’t be until KDE 4.1 or even 4.2. So the first release of the KDE4 desktop series will be still work in progress in some aspects and not so functional like current KDE 3.5 is.
On the other hand, KDE 3.5 is a pretty mature desktop that has been developed and tested for almost 2 years now, the 8th revision, KDE 3.5.8, was released in the beginning of this week, and we’ll likely have a KDE 3.5.9 revision with more bugfixes. Also there are plans to merge the kdepim enterprise branch into the current 3.5 kdepim branch, so we’ll be getting soon a bunch of bugfixes in kdepim, that have the dubious honour in being the second KDE module in Debian with more bugs after kdelibs.
So even if KDE 4.0 is released in december and lenny is delayed, there is not enough time to push KDE 4.0 or even 4.1, into a Debian stable release.