We’ve started working on the “Swift” object model for Island/Darwin, yes, which in the long run will include generating Swift ABI compatible types that Apple Swift can link to, and linking to Apple Swift-generated libraries and frameworks (which would include SwiftUI).
We’re not doing anything specifically for working with or integrating SwiftUI, nor will we, probably, before “SwiftUI 2.0”, which will most likely break everything. But the above, once done (which it’s nit close to being, yet ;), should let you use the SwiftUI APIs.