The "Global FX Division" of AFME, SIFMA and ASIFMA (three global FX Trade bodies)  have written to the US Treasury setting out clearly, why FX Swaps and Forwards should be exempt from Dodd Frank legislation (full letter here)

"warned that pushing currency swaps and forwards onto exchange-type trading systems would be unnecessary, of little benefit and potentially "catastrophic."

The Letter further state:

Mandatory exchange or SEF trading is unnecessary and would decrease liquidity in the FX market.

The letter is well worth reading for all participants in the FX market, and especially those involved in electronic trading and eFX.