You could totally revamp the shard by allowing players to the trade in toons for shard tokens. For say 20% of the value.
For example if you have a 7* toon(330 shards) you could trade in for 66 shards of another character(in equivalent currency)
The character and gear slots would refresh like the other stores but with different stuff each time.
That way players could be more inclined to try out different character formations rather than just trying to follow the meta, as they would be able to start again if it didn't work. Might also help keep people interested mid/late gam as currently if they've invested in farming a formation and they're not arena competitive, they usually just give up