First, I’ll declare right off that I’m okay with Experience Points and Levels just as they are. However, I got to thinking about how BRP advances skills that you use during an adventure by having you roll percentage dice at the end of the adventure and advancing the skill if you roll over it – thus, as you get better at something it becomes harder for you to get better still.
So, what if you had a rating for, say, Fighting and Magic, beginning at 10. Levels in fighting-man and magic-user and other classes are then pegged to ratings for Fighting and Magic (and/or other categories, whatever makes sense in a particular game). So, to become a 2nd level fighting-man, you might need a Fighting rating of 20. At the end of a session of play, you roll your percentile dice, and if you roll above your current rating, you increase your rating by 1 or 2 or 5 points – whatever the Referee is comfortable with. I think 2 would be a good number. When your Fighting rating hits 20, you become a 2nd level fighter. Likewise, magic-users rely on their magic rating. Clerics, on the other hand, might need ratings in both Fighting and Magic, say a 18 in Fighting and a 16 in Magic to advance to 2nd level.
Just a random thought inspired by the idea of “roll to advance”.
Art by Gustaf Tenggren, illustration for Grimm’s Fairy Tales in 1923