Even if it looks like this?

> Caddy-Sponsors: This free web server is made possible by its sponsors: Minio, Uptime Robot, and Sourcegraph

https://github.com/caddyserver/caddy/pull/1866

Yep. So long as they had an agreed max-size of the header, as I don't want to have kilobytes of text added. And an ethical ads policy. "Brought to you by $Hate_Speech_Provider" would be a bummer.

What's wrong with this header?

That PR describes what's wrong pretty thoroughly, some went for the rest of the community's response. Therefore they backed down.