If you use Intel WiDi with Windows 7 or 8, and really like it, you may want to brace yourself before upgrading to Windows 8.1.
Windows 8.1 discontinues WiDi for Ivy Bridge and Haswell – WiDi is still available for Windows 8.1 on Sandy Bridge.
While Intel has aligned WiDi with Miracast, the two have always been basically compatible, WiDi had one ace in the hole that Miracast lacked: USB over Wi-Fi.
The current workaround I can confirm is to deploy WiDi in Windows 8 and then not uninstall it after upgrading to Windows 8.1. Then use Miracast inside the Display settings for display and WiDi settings for USB.
What I can tell you is that this workaround is totally unsupported, but it works because WiDi is still around for Sandy Bridge, which for some reason the 8.1 driver set doesn’t embrace. I presume it will keep working for as long as the Sandy Bridge WiDi payload is maintained by Intel for 8.1 – but you may have to get hacker-grade to extract the WiDi installer. Future versions will probably keep track of if you’re using Sandy Bridge or not.
Personally, my advice would be to move away from WiDi USB if possible, and use Bluetooth or other options. This workaround is for those that really, really need it and don’t have viable alternatives.
I totally understand why Intel has done this, WiDi was a real pain point to maintain. Intel never officially supported WiDi PCs that were not built, shipped, and certified by a top-tier OEM because of all the numerous software payloads that had to be installed and maintained in concert. Miracast in Windows 8.1 is more limiting than WiDi, but gets the job done without the need to manage over a half-dozen driver kits… and keep updating them.
Finally, if you have WiDi-capable hardware that isn’t Miracast-certified, people I’ve talked to assure me the vast majority of modern configurations (again, post-Sandy Bridge) will work… such as the Intel 2230 that is WiDi-certified but not Miracast-certified. Again, I suspect older Sandy Bridge-era Wi-Fi chipsets may be the reason Intel is continuing to support WiDi for SB silicon, but not for Ivy or Haswell.
If you have other WiDi/Miracast questions, I’ll answer the ones I can.
Update: Intel has a utility that will automate the process of removing WiDi on Ivy Bridge/Haswell, and applying WiDi 4.3 if you are on Sandy Bridge. Anyone that had WiDi installed prior to updating Windows 8 to 8.1, should run this utility, even if WiDi was preinstalled by your OEM.