dynamic instance selector

I would like to see an ability to select instances for widgets (and alert rules, etc.) based on other factors than the instance label or glob pattern.  It should be possible to select based on an applies-to-like function using instance properties, instance description and instance group (latter I requested separately some time back).  A good example for this would be a widget that displays all WAN or DIA links in one place.  Selection would be determined either by instance description match (with instructions to the client to ensure those are labeled to cause inclusion) or perhaps by an instance property.  I can do some of this with an API-based tool for widget maintenance, but that would not address all places this should be possible.