The next version will offer multiple currencies for trading.  The same model will apply, where clients exchange directly with one another.  It's going to take awhile to build.

For starters, I'm thinking...

PayPal (USD)
Moneybookers (USD)
LibertyReserve (USD)
Pecunix
LiqPay (USD)

This could transform Bitcoin Market into a true E-Currency exchange, albeit a small one.