Another great idea!
This allows players to slowly earn the ability to purchase boosters or units or whatever.
This also benefits the game, as some players would gladly spend money to speed up construction and other tasks. These microtransactions would help to financially support the game. I suppose that shards could even be spent for many cosmetic items and effects for buildings, units, nation flags, territories, etc. Shards could also be spent to unlock gold difficulty on quests, so that players could skip having to do copper and silver difficulty first. Maybe shards could even be spent to give a temporary boost to XP being earned in quests, or even boost a player's army points during a quest so that an additional unit or two could be fielded to make the quest a bit easier. Shards could even purchase a power-up that could instantly level up a unit, if a player wants to spend money to save time on that. There really are a lot of options for shards!
Hopefully some of these ideas are helpful for developing 2.0!