EtherEx on Ethereum could rapidly make Cryptsy and other crypto-crypto exchanges obsolete.
Could being the big word here. It will not allow real time trading. They say this is an advantage since it won't have HFT. I sympathize with that point of view somewhat, but so far almost every market (both crypto and non-crypto) has preferred real time exchanges.
Overstock's Medici on Counterparty would be pretty big.
Do they have a target date for actually trading? I'm not sure it is realistic to see this fly in 2015, given the regulatory speed limit. Maybe, but look how the Bitcoin ETFs have gotten bogged down.
Ethereum will have a 60 second block time so any contracts traded using it will be pretty quick. After people get gox'd and web services get hacked another dozen times, they may start to see that waiting 60 seconds to make a trustless trade is a tradeoff worth making. In any case, there will be some significant movement of users and volume from centralized crypto-crypto exchanges to decentralized ones. I sure as hell won't be keeping money on centralized crypto-crypto exchanges when I have another choice. That would be a big impact on the space.
On second thought, you're right about Medici. It's probably way too early. Medici could easily be one of those things, like Zerocoin, that seem to just never come into existence.
Perhaps the ETF itself will have the biggest impact 2015 if it even launches.
In my opinion. 2015 is mostly going to be a year of development. It's going to be 2015 in a few weeks. 2015 is already here. Most things are still works in progress.