Do you think this is a place where we could take notes from Estonia? X-Road[0] for example, they call their data exchange layer. I don't know exactly how it works, but it seems to specify some common protocol so various government (and private) services can all work together. I know their system is also very citizen focused, but perhaps something similar could reduce the costs of integrating the specific needs of specific state agencies with the overall set of services a state government provides/uses.

[0]https://www.ria.ee/en/x-road.html