There will be restrictions on borrowing from multiple sources to finance a purchase, and borrowers will have to show that they could handle higher interest rates. That is just good practice for anybody who is taking on new debt.
In short, the regulatory challenges raised by Islamic financial institutions are yet to be resolved in a comprehensive manner. Some regulatory authorities have already started looking into the appropriate regulatory framework. However, there is still quite a distance to travel before regulatory authorities  could come up with a standard and comprehensive set of regulatory prescriptions and supervisory norms for Islamic banking.