This has been a great idea for decades. I want Haystack to be successful just like many other attempts. The early execution seems promising. And I suspect there will be many challenges (e.g. when it's hard to figure out caller/callee,, inconsistent UX preferences across developers, etc). Kudos for taking this on!
Btw I've always thought that this is even more powerful when the screen estate is more infinite than a 2D screen (like in a VR headset).