then maybe put it to a relay that keeps track of compliance fails by event id at least then we'd have a resource to identify the error and how it is malformed

would then just be a typical telemetry option you'd want to nag the user one time for "please help us make the client better" "*sends data to developer relays to improve interoperability of nostr clients" 

 For relays, there is an easy answer: compliance testing apps. Like the check your DNS, or website for SEO applications. I think nostr:nprofile1qqswuyd9ml6qcxd92h6pleptfrcqucvvjy39vg4wx7mv9wm8kakyujgpypmhxue69uhkx6r0wf6hxtndd94k2erfd3nk2u3wvdhk6w35xs6z7qgwwaehxw309ahx7uewd3hkctcpypmhxue69uhkummnw3ezuetfde6kuer6wasku7nfvuh8xurpvdjj7a0nq40 started one.  

 yeah, a test of client is not so easy to do... i have images of macro recorders and using key navigation and injecting it into the input stream via an extension for web clients at least