That's where the distinctions lie - Applications vs Protocols.
I think protocol interoperability is a stretch-goal once at least two such protocols stabilise their respectively, sufficiently, large userbases and have sufficiently different things to offer - The reason I don't expect this to happen (at least not anytime soon) is because developers will eventually go where the incentives are better for them and will build there, making "jumping ship for a different experience" moot, because it'll likely already be there.
As for whether it'll be #nostr, that remains to be seen. But I believe out of the current such protocols, it has the best chance.
It's a well known fact that Bitcoiners have made nostr their home. #Bitcoin is the most decentralised protocol network on the planet, and that was a happy accident, it won't happen again. Given this, most Bitcoin enthusiasts are likely to run a Bitcoin node and will eventually encounter nostr. If one runs a Bitcoin #node, and knows about nostr, they'll also be more likely to running a nostr #relay. The crux is nostr doesn't require that level of decentralisation simply due to a lack of trust necessary against relays in the first place, and yet (perhaps ironically) has the best chance of reaching it. Which in this case won't be an accident.