...
Basic = Roll as normal.
Expert = Allow the character to "take 10" on any check with the skill.
Master = Allow the character to "take 12" on any check with the skill.
Or something like that.
The way I'm thinking to run it would be to let 5e characters invest a proficiency into a skill multiple times.
Proficient = 1 allocation of a proficiency bonus for 1 times your proficiency modifier;
Expert = 2 allocations of a proficiency bonus (or roguish or bardic expertise) for 2 times your proficiency modifier;
Master = 3 allocations of a proficiency bonus (or 2 allocations of a proficiency bonus and roguish or bardic expertise) for 3 times your proficiency modifier;
I think that the current 5e rules are flawed in that they can potentially allow a rogue or a bard to be better at arcana, nature, religion, or survival than a wizard, druid, cleric or ranger.
Fine, bards and rogues become good with skills, but other classes can become good with skills too.
I also see the bard's Jack of all Trades as being opposed to the achievement of skill mastery, though I'd still allow a bard opportunity to master performance.
How would it work, after level 4, to award a skill, language, musical instrument, tool, or vehicle proficiency with each level?