IronPython 2.6 brings in support for attributes through the __clrtype__ metaclass. It doesn't yet allow you to create a .NET interface from pure Python code (although you can implement existing interfaces just by inheriting from them), so *some* C# is still needed for full use of WCF with IronPython 2.6. The dynamic languages team are looking at ways that __clrtype__ could be extended to allow the creation of interfaces in a future release.
In his latest blog post Lukáš Čenovský demonstrates how to create a WCF service from C# and then shows the same code from IronPython, along with the minimal C# still needed.
Until IronPython 2.6, it was not possible to create WCF service host in pure IronPython. The closest way was to create stub in C# and subclass it in IronPython or create the whole service in C# and run it from IronPython. It is now much simpler with IronPython 2.6 although you still have to write a little C# code.