The roads I take...

With bug 350221 resolved on the mozilla.org "trunk", i.e. the main at-the-edge-of-development source copy of the source code, a major step has been achieved in getting suiterunner into a usable state: back/forward history now work, tabs on the browser look how they are supposed to look, new and close tab buttons are what they are supposed to be (minus some problems on Mac which we are investigating).
This means we are getting much nearer to actually switch trunk nightlies over to this toolkit-based SeaMonkey variant which will replace the old xpfe-based version for our Gecko-1.9-based SeaMonkey release. This will be a really major step forward for the suite, bringing it from its dusty old heritage to a more modern system, enabling decent extension management and a lot of other things.
But we are not there yet: The download manager doesn't work (bug 348386) and File > New does not launch a new (second) navigator window (bug 338461) at the moment. Those issues are probably still blocking day-to-day use of this experimental configuration (which can only be tested if you build it yourself or through some very experimental Windows and Mac tinderbox builds). And then, before we really want to switch to using that toolkit-based suite as our default, we want to finish up the profile migrator (bug 329744) far enough that profiles from current SeaMonkey and Mozilla suite can be imported to a "suiterunner" SeaMonkey version. The old installer is broken as well, we are working on a new, NSIS-based installer (bug 351917) as a replacement on Windows and hope to finish it at around the time we're switching to suiterunner on trunk.
Those are the main issues we have for getting that new version in place, lots of smaller ones are known as well (see the dependency list of the main suiterunner bug report). If you want to test those builds, feel free to do so, but read suiterunner wiki page first.

With the current state, we're significantly nearing that new generation of the SeaMonkey suite - and we're continuing our work to really reach the goal of a suite based on the "new toolkit", eventually even XULRunner.
As always, we can use any development help we can get, stop by in our dev newsgroup or in IRC (as noted on the SeaMonkey Community page) if you want to help us.