It is useful to note that a somewhat similar choice has been exercised even in the USA where one is likely to see at least Basel II and Basel I-A entities operating simultaneously. Similarly, even amongst the Basel II entities, it is likely that banks will be implementing various combinations of the multiple options available for computing capital requirements for the three major risks.
Consequently, we may see Basel II implementation as a part of a spectrum of frameworks within which there can be progressive enhancement of quality amongst different categories. It is likely that on implementation of Basel II, some banks might adopt the IRB Approach for credit risk while some other banks in the same jurisdiction, might adopt the Standardised Approach.