KDE 3.5 Alpha source tarballs are up on the FTP servers. It's really Alpha quality so you don't will see a big announcement splash for it. One day before tagging KMail got completely messed up. When it was tagged two modules didn't compile at all. Several modules don't compile with --enable-final, Coolo ultimately gave up on fixing it. This week there were problems with the bandwidth of a server feeding the FTP mirrors so enough reasons for the long delay already. openSUSE going live with SUSE 10.0 Beta and people watching reactions for sure didn't speed things up either.
Two notes about bugs which ship: there is a nasty bug in the Alpha which can crash your whole KDE session when (re)starting the KDE media manager (for example k3b does it after burning CDs) - that's supposed to be fixed in 3.5 branch. And it seems KDE doesn't start up at all for a new user which doesn't have a /var/tmp/kdecache-<userid> already.
If you're brave enough you can try the Konstruct 'Unstable KDE Version' for this release. The more easy and safer way is to play with the "Klax" KDE 3.5 Alpha Live-CD. Please remember that not all planned features are in, and the menu layout, graphics and colors are likely to change before the final release.