Ok so just taking a snippet of what you're addressing here. Let's assume lnaddress is widely adopted across the ecosystem, that still leaves us with the Metadata issue. Is that accurate?
Just brainstorming but seems like from there the solution has to be client side... lnaddress payments do allow for a text field. The client could potentially autofill this with the essential Metadata such as sender, client, show, and track/timestamp when generating the invoice. It would take a meeting of the minds from major clients to implement but could be done i think?