I think the author overlooked that a read-only file system is of absolutely no practical use. If you can't write to it, then there will never be any data in it to be read.
There are plenty of data archival projects that can benefit from DwarFS. Stuff like e.g. old magazines or ROM collections or scanned books/comics that don't have copyright attached etc., don't need modification and if the collection is big enough then the deduplication can reduce the final size of the archive by a lot.