What about being able to control-group the train action itself. Hold tilde [say], click/press train buttons, then press a group number. Units of that type trained by the selected building go into the chosen group. You could do similar things for “all units trained from this structure” or “all units trained of this type” with key variations. No need for option configuration (which might get annoying for competitions on shared hardware).
This would work best with MBS (which hopefully is added alongside UUS, which it seems most people want).