[Suggestion] Prioritized QCache

It would be nice to be able to add items to a QCache such that one can specify their relative priorities and to modify them on the fly. Lower-priority items should always be kicked out of the cache before higher-priority ones. Additionally, have such a priority level that items having that priority get added into the cache even if adding them will exceed the cache limits. Or, more generically, set several cache limits such that there is space that can only be reserved by higher-priority items.