IMO hints need to be provided out of band, that is, not in the SQL query itself. To do this it is necessary to have a way to address every table source, in every sub-query, then one can have hints as a pile of {table source, hint}. Not that this solves the problem of hints rotting, but being able to separate them from the text of the query at least keeps the query clean, and makes is possible to have different sets of hints for different contexts and different RDBMS versions.