You can already create a new user and give them Administrator rights, isn't that essentially the same thing? Would be nice to have the ability to lock the built-in admin account. Also great would be the ability to enable two factor authentication on the built-in admin, but you can set two factor for a user with administrator rights. Perhaps the easiest workaround is to assign a ridiculous password to the built-in admin account and never use it unless in a dire emergency. Or, once you have created a new admin user, you could set the password for the default admin to a bunch of random gibberish typed on your keyboard and never make note of it anywhere. The only problem with that approach is you will never be able change the default admin password as it requires you to know the old one to set a new one. Another option might be to turn on Public Key Auth for the Admin but I'm not sure if that applies to users with Administrator rights or just the built-in admin.
