That would be a lot more difficult (unless you limited support to the subset of Swift which is shared by Objective-C). Objective-C is an extremely simple extension to C, and has a rich runtime API. So any language which can interface with C can interface with Objective-C by using the runtime interfaces.
I successfully used the other way - calling Golang functions from iOS/Swift using Gomobile. It is working now for the new M1 Apple desktop computers too.
