Goldplating

To me this is not an ethical dilema. This is just a case of a team being enamered with technology and doing work that is not requested by the client and, in fact, not wanted by the client. It is out of scope for the project and the team really has no reason to be doing this work. If the team thinks it is important, they should raise it as a scope change and let the client decide if the work should be done or not. It doesn’t matter if the team can archive 6 years of data or 99 years. If the client says they don’t want the work done, then don’t do it.