Should borg assume that it's okay to store unencrypted metadata information of the repositories in the cache without asking?

This question came up in another issue and I'm just posting it separately to improve discussing the topic.

When I first started using borg for a simple backup task, I didn't know about the cache or what it does. I mean, *now* I know about it and the fact that it stores unencrypted metadata. I could have read the internals section in the docs before using borg, but I just didn't.

Does borg assume that its users know that the cache stores unencrypted metadata of the repositories? Does borg assume that its users read the internals section?

Currently, borg assumes

> that the cache is being stored on the very same system which also contains the original files which are being backed up. So someone with access to the cache files would also have access the the original files anyway.

(Quote from the docs FAQ.)

However, I'm still not sure if this should happen silently without informing the user. Additionally, one might use borg to back up an external hard drive: without knowingly changing the cache directory, the cache won't be on the same system as the original files. (Cache in possibly unencrypted home folder, containing information about the files on the backed up encrypted external hard drive.)