For Luck, the main idea is to allow you to build PCs (and NPCs!) that rely a lot on luck instead of skill. Having a character who isn't particularly good at a task, but succeeds anyway simply because of faith, destiny or plain simple luck.
For Renown, the idea is similar but not identical. Renown could mean a feared King ruling absolute. It could mean the casual experience of a grizzled veteran. Or it could indicate how an audience has whipped itself into blind frenzy; where an idol is worshipped regardless of its faults or deficiencies.
Mechanically, both work as regular Abilities (that start on the -2 to 4 scale, can have focuses, etc).
Luck can have any focus really. It is used in place of another Test but only when appropriate (once per encounter is my starting point). The advantage is that you can key it to almost any focus. This means you get to choose your favorite focuses, and instead of spreading them out on several abilities (which all can't have stellar scores), you put them under Luck and then have only that one score to worry about.
Renown works much the same as Luck, except you use it whenever your social standing, fame or notoriety plays a role (and can then take you through all Tests in that encounter). It allows you to rule by fear and awe without being charming or elegant. It is obviously limited in that it mostly concerns itself with Communications focuses.
LUCK FOCUSES
Any: Succeed at almost any task through luck instead of any other ability.
Sheer Luck: Be lucky. Instead of flipping a coin, the GM could call for a Sheer Luck Test, and having the favorable outcome (having a coin purse fall into your knee; not having a boulder drop on your head; choosing the "right" passage in a labyrinth full of traps etc) happen to the character getting the highest result.
RENOWN FOCUSES
Bargaining: Leveraging your reputation to gain favorable deals.
Etiquette: Have your lessers interpret your breaches of protocol as high fashion.
Initiative: Acting ruthlessly in tense situations.
Intimidation: Overawing others with social presence and threats.
Leadership: Guiding, directing, and inspiring others.
Morale: Maintaining good spirits and confidence in yourself or your group. NPCs tend to use this focus more than Player Characters.
Performance: Making an audience convince itself you have an artistic talent.
Persuasion: Convincing others to agree with you.
Seduction: Conveying your superior suitability in the mating game.
What do you think? Any problems you might foresee? Any cool usages I've overlooked?


