This is a suggestion to improve fillable to make it easier to assign multiple values for fillable. This would be useful if a site had different roles, for example if an admin can edit things a user cannot.
To implement this it should just be a matter of a few changes by adding an extra parameter to a few methods for the fillable key, and passing this along when fillable is checked to check against the correct array.
Below is an example of what using this feature would look like.