I like where this is going.
Prison Break- What if a feature was added where, if you attack an enemy capitol with a certain unit setting (like 'evasive'), or use a particular unit type (like 'Special Forces'), or a particular designation (like 'Vanguard'), it would dramatically increase the chance of freeing prisoners? This would represent a concentrated effort to free a prisoner, as opposed to a happy accident of circumstance. Imagine it- one heroic Noble brings a band of special forces into the enemy capitol alone. He will probably have his unit wiped out, and be captured himself, but he does so anyway to free his King, or other dignitary, knowing that he will have a better chance with a small unit of specialists than with a massive frontal assault. It would certainly liven up the action if Nobles had an incentive to attack an enemy capitol alone!
Conversely, perhaps we could build a Prison Break option into the Infiltrator Class to help balance out the new longer prison terms.
As far as luxuries, it would be kinda cool if imprisoned rulers were allowed to write to the ruler channel from prison. It would represent the kind of imprisonment that a leader could work to his own political advantage if he plays it right. Also, I vote yes for optional use of the Academy from prison, and also suggest we throw temples, shrines, and maybe even guilds in there. I think some of these options should become intrinsic (meaning the Judge cannot deny them) depending on a character's position, or honor/prestige, or possibly even his family fame.
This overall concept is a great way to raise the stakes, although I do think some of the larger prison terms are unnecessarily long, and some of the shorter ones not long enough. Here is my suggestion, with Priests and Infiltrators added:
simple nobles with no position: 2 days
knights (nobles with an estate): 3 days
priests: 5 days
marshals, stewards, etc: 7 days
infiltrators: 8 days (I personally think they need a better incentive to not get caught, though they should also have an increased chance of escaping)
landed nobility (lords): 10 days
dukes: 15 days
government members: 20 days
rulers: 25 days
This brings the terms a bit closer together overall.
Anyhow, that's my two cents.