Windows Fall Creators Update (1709) and the IIS Error 503

We finally began the process of updating our Windows 10 desktops to version 1709 (Fall Creators Update) today, and what happened... all of our in-developement websites stopped working.
Pretty much every application pool crashed as soon as we accessed each site for the first time, showing a 503: Service Unavailable error.

In the windows event logs there was the following error event:

Source: IIS-W3SVC-WP
Event ID: 2307

The worker process for application pool 'DefaultAppPool'
encountered an error 'Cannot read configuration file'
trying to read configuration data from file '\\?\<EMPTY>', line number '0'.
The data field contains the error code.

ApplicationPool: DefaultAppPool 
ConfigException: Cannot read configuration file  
FileName: \\?\<EMPTY> 
LineNumber: 0 
            02000000 

Yup, nothing to do but google it.
So, many many people are having hte same prblem.
Turns out it's a known issue. (Who'd have thought.)
Apparently, many users are getting a WAS event 5189 error instead.

To cut a long story short, the official resolution is to execute the following command line operations in a PowerShell windows (With admin rights - "Run as administrator"):

Stop-Service -Force WAS
Remove-Item -Recurse -Force C:\inetpub\temp\appPools\*
Start-Service W3SVC

For the official explanation, including cause and resolution details, see this official Microsoft Support KB article:
https://support.microsoft.com/en-us/help/4050891/error-http-503-and-was-event-5189-from-web-applications-on-windows-10

Update:

Thanks to Bokkeman for pointing out in the comments that the Powershell script has obviously had a few problems, and Microsoft now recommend simply purging the entire folder using a regular command prompt.

"To resolve this problem, manually delete the symbolic links that are created by Windows Update. To do this, follow these steps."

Note Symbolic links can be deleted the same as regular files.

1. Open a Command Prompt window by using the Run as administrator option.
2. Run the following commands:

net stop WAS /y
rmdir /s /q C:\inetpub\temp\appPools
net start W3SVC