I'd argue in favor of at least an annual review process. Have a dedicated "feature freeze, emergencies only" period where you evaluate your existing data structures and queue up any necessary work. The only real hang up here is one of bad management.
In terms of how, it's really just a question of Schema A to Schema B mapping. Have a small team responsible for collection/organization of all the possible schemas and then another small team responsible for writing the mapping functions to transition existing data.
It would require will/force. Ideally, too, jobs of those responsible would be dependent on completion of the task so you couldn't just kick the can. You either do it and do it correctly or you're shopping your resume around.
In terms of how, it's really just a question of Schema A to Schema B mapping. Have a small team responsible for collection/organization of all the possible schemas and then another small team responsible for writing the mapping functions to transition existing data.
It would require will/force. Ideally, too, jobs of those responsible would be dependent on completion of the task so you couldn't just kick the can. You either do it and do it correctly or you're shopping your resume around.