It’s on the list, but to do it in a way that supports all five languages and all platforms takes some additional planning, so I’m afraid this is not supported yet.
You can see the exact overview of what features are implemented at https://docs.elementscompiler.com/Silver/SwiftEvolution/. In general, we’re pretty much caught up with 5.2 on core features, and usually stay in sync/ahead with new versions as the progress, but some of the more corner case or more major-undertaking features are still on the list. Codable is one of those, because essentially we need/way to revise a way to make it usable for all Elements languages and all platforms.
I think I’ll bump priority on this though, as I agree it’s a nice to hav feature.