In an attempt to clarify what these are:
These are not the best place to "test" new features. In many cases unsupported builds have far too many patches to be useful in testing any one patch for inclusion in SVN. Often the interaction of multiple patches creates an environment where it's nearly impossible to tell which patch, if any, is causing problems. This is also why bug reports aren't accepted on any of these builds. Bugs may come from a specific one patch (they should be reported to that patch author), an interaction between two things which aren't wrong on their own (nobody's at fault, and there's no real bug when using the patches on their own as they're intended for until the official environment contains one and it conflicts with the other), OR there's something wrong with official Rockbox. Since it is nearly impossible to say which, and more patches makes it worse, we ask that you test with an official build.
Further, most of these builds are "used" rather than "tested". What this means is that no rigorous attempts go into finding problems with patches, as the intent of most people downloading these builds is to have access to the features, rather than to try to find any problems on specific feature might have. Further more, there is often code in these builds not included in any patch on the tracker that makes it difficult for any testing in the build to necessarily be relevant to applying the patch to official sources.
With that in mind, if you want to see a feature enter mainstream Rockbox, please, take just the patch for that feature, install it, try to find ways that feature doesn't work properly, and provide feedback to that patch's task in flyspray. If possible, investigate the code yourself, and try to improve or fix problems. Ask why a patch hasn't been accepted, and attempt to improve around any hurdles that stand in its way.
I know it seems like unsupported builds are "testing what's coming up before it's out" but in truth they don't provide useful feedback or interaction with the developers actually making the decision, and evidence shows that often when a patch is widely used in unsupported builds little or no concentration goes into improving it for SVN inclusion. We would like to see these features as much as you, but as Rockbox is a community project, we depend on you, the community interested in these features, because that's all we are too: community members spending time on it.