Install-IISAppPool currently uses ValidateSet to ensure .NET CLR is 1.0, 2.0, etc. But Dot Net Core 1.0 needs an AppPool with Managed Code Disabled. See here
Get-IISAppPool returns an empty string for 'No Managed Code' so presumably Install-IISAppPool needs to accept the same. Or maybe have both return/accept 'None' since an empty string is a bit... odd.