I have a well established product with a codebase in purely Objective-C.
I am considering whether to begin migrating this to Swift. Doing the whole thing in one go is not feasible but I think it might be doable bit by bit, reimplementing small parts at a time.
Does anyone have any experience of trying this?
Any dos/don'ts/tips?
Was it worth it?
Hello, @nickmoore
I have ported some parts of one of my apps (P64): the front-end parts, the hardest bits. It wasn't really that hard because I did not use SwiftUI.
Currently, I am in the process of not porting but rewriting the back-end parts (a compiler, code generator, and a math engine) implemented as XPC services.
Have fun with porting. 
The An Approach for Migrating From Objective-C to Swift blog post by Steve Barnegren was a good read.
Yes, this is very instructive.