An Emercoin exchange will be useful in any respect. But if it's p2p then one would usually expect it to be open source.
Absolutely agree!
BTW, MessyCoin wrote:
"Let me know if you have any example where this has been implemented before for any other currency."
There is an interesting discussion:
https://bitcointalk.org/index.php?topic=172705.0Topic: P2P Exchange for bitcoin