If you use Linux as a host, you won't even need a virtual machine. It'll be useful only for non Linux host OSes. On Linux chroot approach will work, saving performance and extra overhead of VMs. Inside the VM it'll run qemu anyway to emulate ARM, so you don't need that extra layer of VirtualBox really.

For those tired waiting, there are other good news. Hopefully Mer/PlasmaActive images for Nexus 7 are coming soon.