Small point of accuracy
The SAP ECC solution was not customised by BCC rather delivered as close to standard by Axon Solutions Ltd. Most of the customisation was integration to other BCC applications, as usual. Service Birmingham was responsible for application management so presumably would still know a lot about how it works.
It didn't take five years to implement SAP ECC so clearly the approach is not well suited to Oracle software and the implementation partners. Similarly conversation from SAP ECC to S/4 HANA doesn't take five years so given the standard Migration tools this was likely a political decision to use another software vendor.
Clearly S/4 HANA private cloud edition ticks the cloud box on a range of hyper-scalers. So freedom from legacy hardware and data centres is readily available.
Biting the hand that feeds IT
