It does mention hashes, the modime support is non-binary - what is supported is a precision. Very large precisions are effectively ignores so rclone sets them to 100y for backends which don't support precisions.
I'll add my two cents:
why not create a local hash/modtime database?
it would be useful for tracking renames and extending some functionalities for unsupported remotes like Mega.
moreover, folks that are using the crypt remote will be interfacing with their cloud providers only through rclone, and never via web or other methods, so that rclone would be confident that nobody modified the file.
rclone could be set up to periodically hashcheck the files, downloading them if needed, to make sure this local db is updated.
does this make sense?