They already ARE subject to regulatory risk
Right, because Bitcoins present the same regulatory risk as dollars.
In the US Bitcoin exchangers are money transmitters. WU is a money transmitter.
WU is registered with FinCEN
WU has a MT license in every state which requires one.
WU has surety bonds in every state which requires one (by the regs it is in excess of $20M face value)
WU has an AML program.
WU has AML training for employees.
WU has a BSA compliance/audit team.
WU collects and records KYC information.
WU blocks suspicious transactions.
WU files various MT related transaction reports with FinCEN.
WU keeps transaction records as required by FinCEN and state regulators.
WU implements per tx and per day limits for customers in accordance with FinCEN and State MT programs.
WU has the legal teams, the size, and the industry contacts to get direct answers from regulators.
Per FinCEN guidance WU is ALREADY doing everything they need to be a 100% compliant Bitcoin exchanger. So yeah if there is ANYONE on the planet which has the compliance structure already in place it would be WU. Still they aren't going to support Bitcoin until it is "game over" for the business model. If/when Bitcoin is is so pervasive that they are losing revenue, they will consider offering bitcoin exchange services not before.