Maybe it's different in other countries but certainly in Australia, banking is a heavily regulated industry, so replacing a banking host (or even parts of a ban

Maybe it's different in other countries but certainly in Australia, banking is a heavily regulated industry, so replacing a banking host (or even parts of a banking host) would require lots regulator approvals and sign-offs (regulator has to sign off all of the technology and the code that will be run - for existing systems, all changes still require approval, but the initial hurdle of approving something new was dealt with a long long time ago).