Yeah the medals system is in place already, and I think achievements would detract from the "sandbox" aspect of BM.
What about random, widespread famines? food dries up thus gold dries up, ergo less troops and vulnerability. The realm undergoing a famine would either have to buy food off of a neighbor or go out and loot food/gold from neighboring realms. I know we already have a food system in place (unless its been changed recently, I haven't been around in a couple years), but why not increase the severity associated with a lack of food? That would bring back the importance and fun in being a trader, create a legitimate RP reason to go to war, be completely random and unbiased, and create obvious incentives to go to war.
Think how awesome it would be to see BoM absorb a starving MI, or to watch a weak CE get torn asunder by an opportunistic Talerium. Similar situations could occur in the FEI and Dwilight, but those continents don't matter....