Filter by number of contacts in a list

A filter that could read the number of contacts in a list would be useful for:

 

* managing event attendance - for example by creating workflows with if/then branches that send different emails depending on how many contacts have filled a form

 

* managing how many contacts can a HubSpot user own

 

* sending "milestone" notifications - eg "Hey, we have reached x subscribers for this event so far..."

 

Please comment with other potential use cases !

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