There's a new app named Keychat that combines Nostr and Signal E2E encryption. https://keychat.io
Yup. I saw it. I've been trying to talk with them about the details for months. The app still isn't released and isn't open source yet. 🤷♂️
It was released and open sourced last week https://github.com/keychat-io/keychat-app