Are there any benefits of using Badoo's reaktive over using expect/actual with RxJava and RxSwift?

The biggest benefit is that Reaktive already exists, so it saves you the work of designing and maintaining your own API. RxJava and RxSwift are not identical and I suspect it’ll be pretty difficult to create a clean expect/actual API on top of them.

RxSwift usage is going to be difficult, if not impossible, inside kotlin until Swift interop comes to native

Oh! I assumed they both align with the same reactive extensions standards. I looked into Reaktive, but I feel slightly uncomfortable that it re-implements all operators. RxJava and RxSwift are well battle tested whereas Reaktive is not.

It has nothing to do with the Rx standards. K/N has direct interop with Obj-C, not Swift. Going the other way, it annotates it's header to make the classes feel nice from Swift. But for direct interop, RxSwift isn't usable from Obj-C (90% sure on that), so K/N won't be able to see it (assuming you wanted to use it in Kotlin). You'd have to add some bridging somewhere (possibly Obj-C)

@basher I see. Thanks for explaining!