Rebuild content on enabled contexts only (feature proposal)

When rebuilding existing content, it should first check for enabled contexts (when global contentblocks.disabled=1 and per-context setting is =0). Then process resources from that context(s).
At the moment ContentBlocks collects all existing resources and checks per-resource if it’s enabled. We have multidomain, multicontext MODx installation with 3000+ resources, which makes rebuilding content in fact impossible (script timeout).
Other option would be to choose context or parent resource ID on which to start rebuild.