What if, instead of levels which require xp, you had proficiencies involving an amount of times you performed x skill.  Because, even though you might "learn" a skill, doesn't mean your good at it.  If you learn the skill to make a bow, you might make it good one time and completely ruin it the next.  But through practice (number of times performed) you gain proficiency.  A master bowmaker would make much better bows, maybe even with added bonuses or properties, which an apprentice bowmaker would not.  This gives incentive for players to improve certain skills.  Obviously some skills would not require a proficiency, they can just be learned.....but for some, this would be a cool feature.