SAP Upgrade
"no easy migration path from one SAP release to the next" is generally an untrue allegation. Rather huge effort has been put into the upgrade path for customers.
HR line of business will have mandated legal change upgrades so finance is required to align which means no case for delay to upgrades. Configuration will be fine, but custom code will depend on the continued use of sap enhancement concepts to be upgrade safe, as we built it, and not creating technical debt through poor practices.
However SAP has been very clear that ECC 6 is EOL 2027 and S/4 Hana is the strategic direction but not a succession product with an automated upgrade path. The BCC decision to Fit to Standard is perfect for S/4 green field implementation.
New infrastructure is required for S/4 but by now the infra would be worn out despite several hardware refresh actions e.g: 20 years / 5 years depreciation cycle.
Whichever ERP is chosen the implementation partners experience and understanding is key to enable making good (low TCO) decisions. The leadership and discipline to Fit to Standard is not easy, and that failure is how to over run by 4 times.