"With multiple code bases touching the same data, schema improvements become nearly impossible."
Few companies have procedures in place that allow this; but it is possible if you have the right procedures.
Sure, but the problem becomes harder the larger you get. Look at almost any Internet-wide deployment, though, and you see the alternative: isolate database schemas behind APIs, and rev APIs and schemas separately, as the situation demands.
Isolating databases behind APIs and rev-ing API+schema separately is not enough. When the schema changes, data must be transformed to match the new schema version. As you point out this takes too long with a large database, and it doesn't account for data consistency.
We have been working on building what we hope are the procedures for this with ChronicDB (http://chronincdb.com). But it turned out harder than it seems, and we are not sure it will quite work out. We'd welcome feedback.
