I think there were some very good ideae that were poorly used postpatch and were forgotten.
The retiring money cost. To actually make use of money, instead of being a simple buffer for upkeep.
The time limit. To set a maximum speed for retirement (if other limits are not enough).
The increasing level limit. And this is really the key feature that should be brought back to cRPG.
If we change the xp curve accordingly, we can make the level required for retiring increase and thus having a gen xp bonus is possible without creating sling effects. What about 25 as a start level limit for gen 1 and it increases by 1 at each retirement ?
If we have a hard level cap (let's say, level 40), people that are gen 15 (so the level requirement for retiring is 40) can retire and the retirement level limit won't go up, (it will stay at 40 forever), but it won't give any more xp bonus (so it doesn't go faster over time).