I'm a huge advocate for SimpleX Chat, but I don't think makes sense to integrate it with Nostr. Nostr has its own direct messaging protocols that are better suited for the specific Nostr environment. SimpleX wouldn't solve any problems.
Discussion
You’re probably right, maybe integration wasn’t really the correct terminology. Maybe a button on the profile to go to that user simpleX. But I guess we can do that with a link on profile.