The submitted github comment also makes that point, this is actually hard to do.
Choice is always better. for people who care\worry, they can change to something more resistant to cracking.
Users will forget their Master Passwords even and because they forgot them they will believe they've been "hacked" and blame you.
Users on Hacker News and similar sites where users actually understand the underlying technology to some degree are the exception, not the norm. Adding options does not help a vast majority of the user base and it complicates your codebase further. Imagine making that change and less than 1% of your users actually use that feature?
