Still I will keep an eye on Bedrock hoping they come up with something cool.
A quick explanation: Bedrock utilizes a number of virtual-filesystem manipulation techniques (chroot(), bind-mounts, a number of our own home-grown virtual filesystems such as a specialized union filesystem) to redirect filesystem calls that could potentially conflict. If two packages need different versions of a given library and they both go to read the library with the same path, they'll be transparently redirected to different files. However, Bedrock doesn't "contain" things as one would typically expect with something like chroot(); the packages can all interact like they typically would. Things which need to be the same for different packages to interact are the same. You can, for example, have an RSS feed reader from one distro launch a web browser from another distro to download a PDF which is opened in a PDF reader from yet a third distro, if you'd like. You can have the majority of the system's packages be from a very stable distro like Debian or RHEL but still get cutting-edge packages from something like Arch or Debian Sid, and have portage compile packages from Gentoo, and still get library compatibility with binary blobs aimed at Ubuntu.
This all works - I'm running it now as my main system and have been long before it ever went public - but it still has a lot of rough edges.
Hope that clears things up.
I've not tried that running Gnome 3.X Bedorck Linux, but I don't see why it wouldn't work. One of the people who used to frequent our IRC channel used to use KDE from Arch with the rest of the system from Debian, if I remember correctly, and it worked fine. I use the occasional Gnome application such as Evince without any trouble.
Bedrock Linux has a number of rough edges at the moment which we're working to resolve in future releases, but once those are done I don't see why you couldn't reach cloud nine :)