I think the discussion is heading toward the right direction.
Obviously disincentives we used to have for old characters did not work. Hopefully incentivizing retiring characters will work a lot better.
Transferring a certain fraction of H/P would definitely be nice. Maybe honour gets cut down (to 25%ish?) but P stays the same? Since Prestige plays a little role in most stuff, it might be a good indicator of how prestigious a certain family line is without checking the family's fame and wealth. Also, it might give people some sort of feeling of continuation of their lineages. (Also they don't have to build up prestige back to be able to choose their subclasses again)
Skill boost: Maybe inheriting 2~3 highest skills? Or maybe even allowing people to redistribute skill might not be a bad idea to encourage them from playing a completely different style of character.
Unit: Maybe allow people to keep their existing unit as well? That way, people can keep their captain as well.
Statue or Monument upon retiring: If the retiring character is old enough + has high honour and prestige + high ranking (duke or gov member) maybe upon retiring, you get to build a statue or monument in the current estate the retiring character is occupying. Of course this will be completely optional since some people probably wouldn't want to make one. Also, it would not be possible for characters who own estates that already have one.
