As a workaround, you can just create multiple 128-character passwords and copy them into the password field. On Mac the shortcut for the password generator is CMD+G.
LUKS now supports 500-character passwords. I agree that you probably won’t gain much after 40 characters or so, but why not allow it if it’s virtually free.
However, expect to run into problems with certain applications and sites. Too many devs don’t expect that anyone would enter a password longer than 30 characters, and I’ve seen really weird stuff happen (e.g., the app truncating your password without telling you where … that is fun).