For regular Swift developers who make iOS apps, yes it's niche.

C++ interop is probably more important for Apple itself.

Swift compiler speed and error reporting are abysmal and improving them would have a much bigger impact. So far it's not getting any better at all.

If I could give up some level of type inferrence and get the build time from 3 minutes to 20 seconds, I would.

It’s not that niche at all if you have a cross platform app or you have a big part of your app that has to interface with metal kernel code, which is C++. There are a lot of reasons why you would want that code accessible from swift as well. And it’s also a big deal in games, communicating between swift and C++ is necessary unless your game only exists on iOS.

Sure, I like the C++ interop and agree that it's important. My point was that 99% of Xcode/Swift app developers will never touch it or even know it's a thing.

Well, in fairness I would probably take "error messages point to a file location" over "lifetime annotations for C++ FFI".