My suggestions is to make shards of magic as acquired via sundering magical items count as a summoning reagent relevant to the elemental plane it represents.
I think it would be fairly balanced, given that reagents are expended and otherwise are extremely rare to come by, also requiring a reconfiguration of the conjurative focus each time it is to be used.
Is it really such a bad thing to have variety more accessible?
If there is concern in it becoming too common, perhaps it can be resolved by making only a certain quality of shard and above register as a reagent.