I do understand that this topic has been covered in some way at StackOverflow but I'm still not able to figure out the exact answer: can I treat IronPython as a Pythonic replacement to C#?
I use CPython every day, I love the Zen :) but my current task is a Windows-only application with a complex GUI and some other features which I would like to implement using .NET.
That depends on what it is about C# that you need, and which needs replacing.
If the reason you use C# is that you need a reasonably high performance statically typed language then no, IronPython is likely not going to be a replacement.
If the reason you use it is simply "I need something that runs on .NET and can access .NET libraries", then yes, any language that runs on .NET can be used to replace it.
If you use C# because you're working with a team of programmers who only know C-like languages, C# might also be difficult to replace with IronPython.
It depends on what characteristics about C# it is that you care about, and need to find replacements for.
Can I treat IronPython as a Pythonic replacement to C#?