We've done some experimentation with it, and it's possible, but it required "if pwsh do X, else do Y" in several of the core connection methods (around hash calculation, etc), as some .NET things have moved around since .NET 4.0 on the oldest platforms we support.
Just out of curiosity: why is it that you want Ansible to target PS Core? We did our initial experiments in the context of trying to support Nano Server, but base Nano Server images in 1709 don't even come with PS/WinRM, and Microsoft's plan is to continue working with Windows Powershell ("big" Powershell) for the foreseeable future.
-Matt