What's "this kind of work"? :) The company I work for does reconciliation as a service, something that's pervasive in finance. We support customer-defined schemas; in fact that's one of our selling-points. I could start talking about the kinds of things we've done with MySQL to make this perform well - it's not difficult, just a bit unorthodox.

Anyway, the diversity in customer schema leaks out into the Hadoop schema, where we'd much prefer to give customers data using column names they're familiar with, and we also want to give them rows from all their different schemas in a single table (because many schemas have overlap by design). The superset of all schema columns is large, however. The problem can be overcome with more tooling - defining friendly views with explicit column choice - but having the option to implement that (and go to market sooner), vs a requirement to implement that, adds up to a distinct advantage for tech that can support the extra columns.