We are thinking to move away from Django and separate the backend and frontend.
The backend is straight forward as I have done it plenty of times by exposing it as a Python RESTful API.
Whats new to me is the thin client part.
Theoretically I could just write HTML and plain javascript to talk to the API. 
Is there a macro-framework that would help me to achieve that? Beside AngularJS, what other thin client frameworks could I utilise without reinventing the wheel?
If I understand what you're trying to do, you might be looking for something like jQuery. It's a subtle JS framework that will make it easier to talk to your Django API, especially using Ajax and JSON.
How to move from Django to REST-API/Thin Client?