Course it is. It's built on open standards. The first App launch is in closed beta to test and fix the bugs. But #pubky standards are and have always been open. Any number of apps can build #pubky. The reason is that it offers verifiable censorship-resistance. ie 6 million servers vs 6 servers. Any nostr devs that care about censorship-resistance should integrate #pubky open standard. But most nostr devs prefer DNS right now. Maybe that will change!