Lets say in theory someone is creating a bitcoin/altcoin trading website/app.
What would make it perfect? How could it better than the sites we already have?
We can debate on the 'features' an exchange should have, but what makes an exchange 'perfect' is the trust issue. One really has to have that confidence in the exchange that it would not be involved in insider trading, won't run away with their money etc.
Another requirement would be decentralisation.
If there is something that establishes a transparency between users and exchange to establish this trust and if it can be decentralised, it will be a near-perfect scenario.