Not practical, the currency system we have for these types of materials is not meant to be directly exchangeable by design. Enhancement Cores are meant to be obtainable from all sources, while Enhancement Prisms and Ascendant Shards are only obtainable from certain endgame sources. These resources are not difficult to obtain, but require playing certain types of activities. Having a system to break down these materials would either a) over-inflate the economy with Cores or b) have such a low exchange rate that it would be meaningless to exchange. The best thing to do with your Shards is to use them, that's why the limit was put in place. If you have maximum shards, masterwork an exotic or a favorite legendary armor set.