The reason it is being change is due to the new core banking system implementation, which means all the CIMBs across the region will share the same IT platform and thus account number. This is to facilitate cross border trades / transactions.

It is not done for fun and if you rage now, you wait until Maybank, RHB and the rest does the same. The reason they are not doing it yet is simply because their system is not ready. It was also done during the festive season because that is the time most businesses do not crucially rely on the banking system (as many is closed for holidays) thus the criticality and risk is lower.

You will be surprised. Consumer banking, while remaining the bread and butter for banks, pales in comparison to investment, commercial, private wealth, SME, etc etc... This is done mainly for businesses (your MNCs and such) as well as to enhance the bank's back end system as there were a lot of systems that have been in used since the 80's. Many systems are just applied on top of older systems or small improvements.

I can bet you they will follow as I have some first hand knowledge of those .. I think Maybank is probabaly just a year or so behind? There are some Tigers here that might be able to shed a more accurate light on the timeline. Maybe they can do it much better than CIMB, but they should since they would be able to learn from whatever CIMB has done.