Cost-based delay for (other) maintenance operations

We've run into multiple situations recently where clients were effectively unable to run CREATE INDEX or REINDEX (CONCURRENTLY or otherwise) due to the load that they imposed on the system, mostly in I/O. I'd like to propose a cost-based delay system for maintenance operations such as these, paralleling the system for (auto)VACUUM. Before I pull together a code proposal, I wanted to preflight the idea to make sure it has not been considered and rejected already, or find out if anyone is working on it already.