I am looking forward to the latest edition of OS X macOS called “Sierra”.
Also I definitley want to get it running on my Xeon machine. Currently I am however relocating which limits my time to look into this hobby. I got my hands on the dev DMG however already, and will look into booting it in VirtualBox.
Update:
I finished installing Sierra in VirtualBox. I basically prepared a ISO similar to El Capitan discussed here (while running it on my MacBookAir): http://www.insanelymac.com/forum/topic/309654-run-vanilla-os-x-el-capitan-yosemite-or-mavericks-in-virtualbox-5010-on-a-windows-host/
Some screens: 
(hmm is this really 10.12 ? Looks like El Cap.)
(OK it is 10.12)
(Don’t think Siri works in VM – but sure)
(Finished – good to see Spotlight search still exists and Siri is next to it)
OS Xeon 