Sketch is really awesome, and serves different purposes. Domical is just an interpreter for the iodide notebooks, which are designed to be portable and execute all kind of languages: js, python (those crazy folks compiled the full interpreter and f numpy in WASM) and now OCaml.
I can see that sketch has really a lot more features.
A key feature of iodide is its simplicity and portability: the whole notebook is written in a readable format looking like markdown and called jsmd. Take a look at the source code of the page to better understand.
So definitely we have a lot to share on our respective projects, even if I am not one of the main contributors of iodide (I just did the OCaml part).
If you want to continue this discussion, my email is on my homepage :)