I have found a solution to the tsadmin problem. Copy these files from a 2008 server to the Windows 2012/8 computer under c:\windows\system32

tsadmin.dll
tsadmin.msc
umcRes.dll
wts.dll

Then import these registry settings and you have Tsadmin.msc working again! :) 

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MMC\SnapIns\FX:{3FCE72B6-A31B-43ac-ADDA-120E1E56EB0F}]

"ApplicationBase"=hex(2):43,00,3a,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,00,\

  73,00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,00,00

"About"="{00000000-0000-0000-0000-000000000000}"

"VersionStringIndirect"="@C:\\Windows\\System32\\umcRes.dll,-106"

"ProviderStringIndirect"=hex(2):40,00,43,00,3a,00,5c,00,57,00,69,00,6e,00,64,\

  00,6f,00,77,00,73,00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,\

  5c,00,75,00,6d,00,63,00,52,00,65,00,73,00,2e,00,64,00,6c,00,6c,00,2c,00,2d,\

  00,31,00,30,00,32,00,00,00

"NameString"="Remote Desktop Services Manager"

"HelpTopic"=hex(2):25,00,73,00,79,00,73,00,74,00,65,00,6d,00,72,00,6f,00,6f,00,\

  74,00,25,00,5c,00,68,00,65,00,6c,00,70,00,5c,00,74,00,73,00,5f,00,6d,00,61,\

  00,6e,00,61,00,67,00,65,00,72,00,2e,00,63,00,68,00,6d,00,00,00

"AssemblyName"="tsadmin"

"RuntimeVersion"="v2.0.50215"

"Description"="Manage Remote Desktop Services sessions"

"DescriptionStringIndirect"=hex(2):40,00,43,00,3a,00,5c,00,57,00,69,00,6e,00,\

  64,00,6f,00,77,00,73,00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,\

  00,5c,00,75,00,6d,00,63,00,52,00,65,00,73,00,2e,00,64,00,6c,00,6c,00,2c,00,\

  2d,00,31,00,30,00,34,00,00,00

"LinkedHelpTopics"=hex(2):25,00,73,00,79,00,73,00,74,00,65,00,6d,00,72,00,6f,\

  00,6f,00,74,00,25,00,5c,00,68,00,65,00,6c,00,70,00,5c,00,74,00,73,00,5f,00,\

  6d,00,61,00,6e,00,61,00,67,00,65,00,72,00,2e,00,63,00,68,00,6d,00,00,00

"NameStringIndirect"=hex(2):40,00,43,00,3a,00,5c,00,57,00,69,00,6e,00,64,00,6f,\

  00,77,00,73,00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,\

  75,00,6d,00,63,00,52,00,65,00,73,00,2e,00,64,00,6c,00,6c,00,2c,00,2d,00,31,\

  00,30,00,33,00,00,00

"IconIndirect"=hex(2):40,00,43,00,3a,00,5c,00,57,00,69,00,6e,00,64,00,6f,00,77,\

  00,73,00,5c,00,53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,75,00,\

  6d,00,63,00,52,00,65,00,73,00,2e,00,64,00,6c,00,6c,00,2c,00,2d,00,31,00,31,\

  00,31,00,00,00

"FxVersion"="2.0.1.7"

"Type"="Microsoft.TerminalServices.Monitor.SnapIn.TSManagerSnapIn, tsadmin, Version=6.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"

"FolderBitmapsColorMask"=dword:00000000

"ModuleName"="tsadmin.dll"

"Provider"="Microsoft Corporation"

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MMC\SnapIns\FX:{3FCE72B6-A31B-43ac-ADDA-120E1E56EB0F}\NodeTypes]

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MMC\SnapIns\FX:{3FCE72B6-A31B-43ac-ADDA-120E1E56EB0F}\Standalone]