I’ve been hoping for a miscellaneous non-N section for a while as others have mentioned above. For those interested and members, I published an expressions/idiom companion deck in Kitsun recently based on the title book of 180 common expressions. I’m using Kitsun’s dictionary build and productive input features+ key expression audio and book has the full conversations for context (with audio) so I encourage both for those interested. I attempted to give notes on context for necessary items as well.
I suppose there is a fine line between grammar point/expression/idiom but there are certainly differences and don’t know if BP needs to have 12 sentence levels per each point (though would still welcome them). Something like あっという間に or あわよくば are definitely expressions (which I just added to the deck). Many of these function as basic grammar, just idioms can be ironic/funny or have historical cultural origin than may seem abstract. Given how common these are, I’m trying to reshape my studies to include them better.