I am not certain that achieving peerage is not a popularity contest. Consider the following mechanic:
Monarch has command to raise and can do so as they see fit. -> Character wishes to be raised, Monarch has decreed it costs them <x> prestige/support (paid to the Monarch) -> Significant number of Nobles oppose ennobling Character, threatening to withdraw their support of the Monarch -> the cost in prestige/support over time versus the one time gain causes Monarch to reconsider, Character is not made a noble.
The example is not perfect, but it illustrates how the system could be completely in the hands of the players without even rules/regulations (other than the ratio that governs how many nobles the Monarch can raise). How it could balance itself, even.
