I just got the dell xps 12. Messing around with the widi, I reached the point where trying to install the widi software on the xps 12 caused an abortion of the installation and the error "not compatible with your platform". Yeah, whatever.....
Anyway, reformatted it back to factory settings.
Using a ptv3000 from netgear (Push2tv)
the wireless display software after factory reset was 3.5.40 or something like that., wifi was v15.6.1
Was then able to download widi 4.0.18.0 from intel and it allowed for "upgrade the software". Previously it would give me that non compatible with platform error above when I removed the intel widi and then tried to install it. Guess removing it was a big no no, as I couldn't even install dell's original widi softwareafterwards due to the non compatible with platform error as well.
Updated the netgear firmware to 2.2.15 (was at 2.2.9). Set it up as instructed from netgear. Using to windows key + P combo, I got the external display thing, made it mirrored from laptop screen (not extended like it says in the ptv3000 manual) and it worked. So far it's looking good except for that slight lag. Was trying to stream from my main computer to the laptop to the netgear ptv300 (waaaay too much streaming, was choppy though sound was present). A movie actually on the laptop itself however ran fine.
Doesn't beat the mini hdmi to hdmi cable though in terms of speed, but who cares, the option was there, got it working, I'm ok with that. All my tvs are hooked up to computers anyway throughout the house, so it's not like I really needed it. But knowing it was there and not being able to get it working was really bugging me:-)