as i see it, levelling up heroes is kinda hard right now since there's usually not enough XP around to get more than your sov to a decent level. stacking several champs doesn't help as the XP is split among them, so instead of one high level guy and several low levels, you'll end up with several mediocre heroes.

i believe one of the goals with this expansion was to tie heroes and empire development closer together (with the fame system where building impressive stuff attracts heroes etc.), so my idea is to take that approach one step further and give us an option to basically buy hero XP for gold.

an implementation of this idea that makes some sense within the context of the game would be the adventurers guild. the guild could work similar to other city improvements that unlock consumables in the shop (like scroll scribe and alchemist guild). there are already random drop books that give a certain amount of XP to your heroes, so my suggestion is to make those books available for gildar at the shop once you have the adventurers guild. it would be very expensive to buy extra levels for a guy who is already very experienced, but you could probably afford to buy some extra levels for low level heroes and also a nice way for levelling up governor type heroes (they basically sit in their city doing their government stuff and the empire pays for their advanced training without them having to go out and fight monsters).

the available books and prices could also be dynamically tied to the level of your sov/other heroes - if one of your guys is an epic level 20 adventurer who casually kills dragons etc., the guild might have more powerful (more efficient - more XP/gold) tomes available then at the beginning when your highest level guy still struggles defeating bears and ogres. 

thanks for reading and let me know what you think about the idea