Caching should be possible as long as all the models use the same shared cache. The models don't even need to be running on the same server if the shared cache is distributed.

I have a feeling people reading this are thinking that a model router would be used to route between different providers. And in that case, a shared cache would be impossible, although some caching would still be effective. I think, ideally, a router like this is in front of a set of models hosted in one place.