There are 2 parts:
1/ List of dynasties, with their respective Dynasty Prestige in the ledger: I agree. (But there is no "Dynasty Piety", so I don't know what you are talking about with that.)
2/ Added mechanic for Dynasty Prestige: actually, your Dynasty Prestige already adds to your Character Prestige at birth, which boosts opinion of people and eases diplomacy, so what you are asking for is already in the game. See:
http://www.ckiiwiki.com/Prestige#Dynasty_Prestige
Side note: you may be confused because there are 3 closed but distinct notions:
-- Character Prestige (and Piety): represents *your* personal standing. Adds to your Dynasty Score on death, but not to your Dynasty Prestige. Increased or decreased by your actions.
-- Dynasty Prestige: represents the standing of your dynasty. Adds to your Character Prestige on birth, and to your spouse's Character Prestige on wedding. Increased on death of any dynasty member by their titles held, also counting the current titles of living dynasty members.
-- Dynasty Score: game objective with no effect on gameplay. Increased on death, by your Character Prestige + Piety. This is what is displayed on the End Game screen.
Hope that helps.
EDIT: corrected some slight mistakes and clarified.