Used to play a trading card game on my phone a few years back. In game trading was a mess. Players were selling stuff for real money, and there was a lot of bad hacking resulting in cards being stolen from other players and then sold for a ton of money on neoseeker or somewhere else. Only 1 account per device was allowed, but before bluestacks loophole was closed it was a mess, and even after it was still an issue.
Trading characters, and shards is not a good idea in my opinion. If it was up to me I would try to find a way to expand on the gear exchange a bit, but would have to be very careful to make sure it would not be exploited. Currently, EA's solution has been excellent at that so any change would have to be well thought out to not become an issue.