If you still have Windows 2008 R2 you can install PowerShell 4.0 on it.
PowerShell 4 is part of Windows Management Framework 4 (WMF 4). There's a known issue that WMF installer will not check all prerequisites are installed, will continue to install and leave PS installation corrupt.
NET 4.5 needs to be installed before installing WMF 4.0.
If you installed WMF 4.0 first (like I did) you can rollback and follow up procedure below to fix.
This worked for me:
- Uninstall all KBs which are part of WMF 4.0 (you can find them listed here)
- Install NET. 4.5
- Install WMF 4.0
- Enjoy PoweShell 4
That's it. Now you can get back to 2013 with Win 2008 R2.