While it would be better to support all possible currency tags the trade system supports, a simpler option would be to make it possible to edit the currency list that can be used as prices, for example I'd like to set exalted-shard as price for my chaos to buy shards without messing with the code manually.
Another option, custom currency tags might be typed directly from UI, if it's not going to mess up the current simplicity.
While it would be better to support all possible currency tags the trade system supports, a simpler option would be to make it possible to edit the currency list that can be used as prices, for example I'd like to set exalted-shard as price for my chaos to buy shards without messing with the code manually.
Another option, custom currency tags might be typed directly from UI, if it's not going to mess up the current simplicity.
Supported tags: https://www.pathofexile.com/trade/about http://currency.poe.trade/tags