Addition of plate armor, halberds, cannon, and muskets. Early Renaissance ****.
Via a tech tree.
These would either be slowly unlocked at specific years in the game, or factions would have to build buildings in their towns and actively research them in order to contribute to their discovery. Ability to toggle on/off whether or not you want a certain tech to be researchable (so you wouldn’t be forced to play with muskets at the end of a 500 year long game).
but tbh I’d rather it be an official expansion. Just some mechanic that lets our nations feel like they’re evolving. Probably out of scope for a hack and slash rpg, but a boy can dream