From an API perspective it could be "put this code in an <iframe> every X tweets" for basic web-based clients, and/or promoted tweets could be tweets with extra

From an API perspective it could be "put this code in an <iframe> every X tweets" for basic web-based clients, and/or promoted tweets could be tweets with extra data for tracking. Enforcement can be done with a banhammer — big profitable apps won't risk getting booted over non-compliance, and non-profitable apps are non-profitable and not worth chasing over this.