And Nostr DMs are simply unsafe at the moment.
SimpleX could use Nostr for discovery, but it requires support from clients first. It would be very easy to add a field for SimpleX addresses, as was made in this proposal: https://github.com/retrnull/garnet/issues/8
Once this is added, SimpleX could add in-app support for discovery via Nostr, similar to how many Lightning wallets already do it.
Discussion
As someone nu to nostr, that's what I was wondering