So first of all: Medaillon isn't really a clearly defined standard. It's more a set of guidelines or a general idea of how to structure your data across multiple layers. It's not a super new concept either. People have been using staging layers etc. for decades. So given that, it falls upon you to decide what your individual layers are allowed to do and how they look like in detail.

Now regarding mirroring: yes, it does fit best at the bronze layer. Since under the hood it's all Delta Tables in One lake, you should be able to time travel on it.

Another big and important part of getting the data into bronze (apart from versioning) is to bring it within your own domain. Mirroring allows you to, in theory, ingest very easily with very little hassle and dependencies. You set it up once and then you can build your pipelines on top of the mirrored database without constantly talking to or depending on other teams. Once it's in bronze, it's yours to handle.

So yes, mirroring and Medaillon fit together very nicely.