“These boundaries will linger in people's mind for quite a long time (at least down to the districts)” —> Yes I totally agree, and given that the districts are mostly well known, and there are only 704 of them, it makes sense to keep them as boundary=historical.
But also keep 10k communes (including nearly 7k defunct), that is very IMPRACTICAL. Keeping them means you have to maintain them, if it is an existing commune then at least people will pay more attention to it and will notice sooner if it is vandalized. Defunct communes, most of which are not well-known, if vandalized, cannot be easily detected.
