They could make cash from the fluctuations in Bitcoin's price, as opposed to transaction fees. This would force them to create an exchange and act as a wallet. This would not only help PayPal business wise, but it would help the people who are interested in Bitcoin get involved that aren't too sure about about digital currencies. If they don't do it, they'll be out of business from someone that will.
As I've stated before, by promoting Bitcoin in any way they will inevitably weaken the value of Paypal as a payment system. Unless they perceive that the revenue from running a Bitcoin exchange (which will be costly to get the appropriate licensing in place as well as legal agreements in multiple countries) will greatly outstrip the losses from a shift away from Paypal I'm doubtful they would actually do it. Not to mention, the market that Bitcoin reaches is still tiny in comparison to what CC/PP reaches at the moment.
