If the general REST API in Swift is good then WeatherKit can be integrated into Swift apps as easily as any other service. If it's not easy then improvements to the general REST API could be considered.
No idea if they are implementing those kinds of enhancements but it’s no surprise that a native SDK would be provided.
Also, how would they implement the privacy preserving black box location implementation with a REST API? There is no need for the app to ask for or receive specific location details by using this SDK.
What is your differentiation criteria between anticipating a "huge" boon versus a "regular" or "modest" boon"?
Would you like to know more? If so just shoot me an email.
Also not having to deal with web requests (client, retry logic, polling, etc)
So you can use it without having to deal with the low level detail of HTTP connections.
Client library frees you from that.